Archive for the 'Mozilla' Category

Running Extension Code In Another Process

Friday, December 3rd, 2010

In order to support running Jetpack-style extensions in another process, Firefox 4 has support for running arbitrary JavaScript code in a separate process. Although this code was designed primarily to support the Jetpack SDK, Firefox and extensions can use this support to run arbitrary code in a separate process.

Running code in a separate process has advantages similar to running code in a separate thread. The running code will not block the main Firefox user interface. An added advantage is crash protection: if the code causes a crash, it will not take down the entire browser. There may also be some performance benefits from separating the garbage collection heaps and avoiding XPCOM overhead.

The basic steps to start a subprocess and run code in it are as follows:

var process = Components.classes[";1"].
process.evalScript("Put your JS here");
// When you are done with the process, you should explicitly destroy it.

Of course, running a script in another process isn’t that useful unless you can communicate with it. This is accomplished by passing messages back and forth. To send a message to the remote process, use process.sendMessage:

process.sendMessage("messageName", param...)

To receive messages from the remote process, register a receiver function:

process.registerReceiver("messageName, function(messageName, argument...) { ... });

The remote process has access to a similar set of global functions, as well as the ability to create sandboxes and use ctypes. For more information about the full capabilities, see the Mozilla Developer Center documentation. Note that code running in a jetpack-style process does not have access to XPCOM, because XPCOM is not started in the jetpack process; it runs code using only the JavaScript engine.

If an extension is using ctypes to work with third-party code or OS libraries, I strongly encourage that extension to consider running the code in a separate process for crash protection. If an extension has long-running or computationally expensive tasks, it might make sense to move those into a separate process as well. If nothing else, it will make it much easier to measure the CPU and memory usage of that code separate from the rest of Firefox.

Bank of America online “Hardware and Software Requirements”

Wednesday, December 1st, 2010

Bank of America is asking me to agree to a “Electronic Communications Disclosure” which includes the following text:

(5) Hardware and Software Requirements

While you may be able to access and retain the Communications using other hardware and software, your personal computer needs to support the following requirements:

For Online Banking:

  • An operating system, such as:
    • Windows NT, 2000, ME, XP, Vista, or Win 7; or
    • Macintosh OS 10.x
  • Access to the Internet and an Internet browser which supports HTML 4.0 and 128bit SSL encryption and Javascript, such as:
    • For PC using Windows NT, 2000, ME, XP, Vista, or Win 7
      • Microsoft Internet Explorer 7.0 and higher
      • Firefox 3 and higher
      • Chrome 3.0 and higher
    • For Macintosh using OS 10.x
      • Safari 3.0 and higher
      • Firefox 3 and higher
      • Chrome 4.0 and higher

For Merrill Lynch brokerage websites:

  • You must have access to a personal computer with browser software such as Microsoft Internet Explorer; Adobe Acrobat Reader; and Internet access (at your cost).
    • Browser and reader versions necessary to view the Merrill Lynch brokerage websites are as follows:
      • Microsoft Internet Explorer version 6.0 and later
      • Firefox version 3.5 and later
      • Safari version 3.2 and later

Most Communications provided within Online Banking, Merrill Lynch brokerage websites or at other Bank of America websites are provided either in HTML and/or PDF format. For Communications provided in PDF format, Adobe Acrobat Reader 6.0 or later versions is required – A free copy of Adobe Acrobat Reader may be obtained from the Adobe website at
Download Adobe Reader for free. Link opens new window.

In certain circumstances, some Communications may be provided by e-mail. You are responsible for providing us with a valid e-mail address to accept delivery of Communications.

To print or download Communications you must have a printer connected to your computer or sufficient hard-drive space (approximately 1 MB) to store the Communications.

Does this entire section say anything other than “You have to have an operating system and a web browser, and sometimes a way to view PDF files, and here are some programs you can use.”? Why bother writing it at all?

Software Integration Is Not Evil

Monday, November 29th, 2010

Asa is wrong, and he’s being obnoxious about it to boot. What Google, and Apple, and Microsoft is doing is called software integration, and in general it’s very good that iTunes, Google Earth, and Windows Live are adding Firefox integration into their software. They are installing plugins and/or extensions using the recommended methods so that all NPAPI-capable browsers can see and load them. This is not “Google being bad”, this is Google following Mozilla’s recommendations for browser integration!

It’s true that Firefox should give users more control over integration software that is found on the system, and we’re working on prompting users whether they want to include that integration as part of Firefox. But claiming that Google, Apple, and Microsoft are somehow being evil is stupid and short-sighted. The problem, if there is one, lies entirely with Firefox, not with the software which is doing exactly what we ask of them.

Asynchronous Plugin Layer Painting

Thursday, November 18th, 2010

Firefox 4 implements a new strategy for painting windowless plugins. This should result in improved performance and responsiveness when users are visiting sites such as Hulu and Vimeo which make use of windowless Flash to render their videos.


On Windows and Linux, there are two basic modes in which plugins can render, windowless and windowed. When a windowed plugin instance is requested, Firefox creates a native widget; the operating system delivers native events, including paint requests, directly to the plugin window. This is simple, but it has a significant disadvantage: the plugin doesn’t participate in normal web layout. This means that the plugin cannot be transparent, and CSS effects such as opacity and most transformations cannot be applied to the plugin. Youtube currently mostly uses windowed plugin instances for rendering their videos.

Windowless plugin, on the other hand, do not have a native widget. Instead, events such as mouse and keyboard events, as well as requests to paint the plugin, are received by the browser and forwarded to the plugin using the NPP_HandleEvent API. Hulu and vimeo both make use of windowless plugin instances. Any Flash plugin with the wmode=”opaque” or wmode=”transparent” attribute in their <embed> or <object> tags is using windowless mode.

Asynchronous Painting

In Firefox 3.6 and earlier, every time the operating system asks the browser to paint its window, we synchronously walk the layout frames and ask each frame to paint itself. When a windowless plugin frame is asked to paint, it synthesizes a WM_PAINT event and sends it to the plugin using NPP_HandleEvent. This is straightforward, but it does involve a blocking call and process round-trip for plugins which run in a separate process.

In Firefox 4, we don’t paint the plugin directly to the screen. Instead, as soon as the plugin is visible we ask it to paint to a retained buffer (an X surface on Linux, and a shared-memory DIBSection on Windows). We retain the pixel data for the next time Firefox is asked to paint. When using D3D rendering, we can eagerly upload the plugin data to a texture, and the plugin texture is composited by the graphics card and GPU.

A Behavior Change: Opacity on Windows

On Windows, the new asynchronous painting API has one significant side effect: plugins responding to a WM_PAINT message must be aware of opacity. The device context which is passed to the plugin is backed by a DIBSection with an opacity channel. Certain Windows Drawing functions, such as the DrawText function, are not aware of opacity and will incorrectly overwrite the opacity data, leaving black splotches where transparent text was intended. Windows drawing functions such as AlphaBlend are the correct way to draw while preserving transparency information.

Most Flash and Silverlight sites work correctly with this new function, but there are a few Flash features which continue to use the old Windows APIs. This bug shows itself in current Firefox nightly builds as black splotches where text should be painted, and is being tracked by Mozilla bug 611698; we are working with Adobe to resolve this issue before Firefox 4 is released.

Testing Wanted

Although our implementation of asynchronous painting passes all of our internal tests and appears to work well in general, the web is a big place and we can’t test every page or plugin available on the web. We would really like people who develop with plugins or use plugin-intensive sites to test Firefox nightly builds and report any bugs which you see! These builds are updated to our most recent Firefox each night, so you will always have the latest and greatest features (and sometimes bugs) to experiment with.

Note to Flash Authors

If your site uses wmode=”transparent” but your Flash application is not actually transparent or translucent, you can get better performance in both Firefox and Chrome by switching to wmode=”opaque”. Please use wmode=”opaque” for content which does not need actual transparent behavior.

Adobe Symbol Server: How Adobe Could Address Crash Issues

Thursday, February 18th, 2010

Since crash bugs are a top priority within Adobe, there is one relatively simple step Adobe should take which would make it much easier for everyone else to help Adobe track and diagnose crashes: implement a symbol server.

A symbol server is a public web server from which developers can fetch debugging information (PDB files) for released binaries. The Microsoft debuggers have excellent support for automatically pulling down symbols as they are needed in the debugger. Mozilla runs a symbol server for Firefox nightlies and releases, which is invaluable for people debugging and profiling Firefox without having to do a custom build. Microsoft runs a symbol server which contains debug information for Windows and many other Microsoft products, including the Silverlight plugin.

Debug information is not simply a way to get symbolic information from Flash. It is necessary in order to get any useful stack trace of the Mozilla code which is calling Flash. A common compiler optimization called frame pointer omission (FPO) avoids storing the frame pointer in the x86 EBP register, freeing that register up for general use. In order to walk the stack of this optimized code, the debugger has to query the frame size and frame pointer information from the PDB file. When debug information is not available, stack walking doesn’t produce usable results.

As an example, take the current #3 topcrash for nightly builds of Firefox (mozilla-central). The signature for this crash is NPSWF32.dll@0x1e7fe4. The stack traces from Mozilla’s crash reporting system are completely opaque:























Even worse, the crash signature depends on the particular version of Flash that is installed on the user’s computer. We can’t tell if a particular crash signature is fixed by a new revision of flash because without symbols we can’t correlate crashes between different versions.

As part of developing multi-process plugins for Firefox, we are constantly dealing with unexpected plugin behaviors. Whenever we encounter a problem which can be reproduced in both Silverlight and Flash, we’ll always test with silverlight, simply because Microsoft makes Silverlight symbols available through their symbol server and therefore we can actually step through their code and ours in a debugger.

Adobe should set up a symbol server for their three main plugins, Flash, Shockwave, and Acrobat. By implementing this simple tool, Adobe could help all browser vendors and interested hackers to help identify and fix bugs. If Adobe is concerned about using full debug information to reverse-engineer details of their code, there is a way to strip the PDB files so that only frame-pointer information and function names.

Multi-Process Plugins on By Default

Wednesday, January 27th, 2010

Out-of-process plugins (OOPP) are now on by default in mozilla-central! Starting tomorrow morning, the mozilla-central nightly builds will load Flash and all other plugins in a separate process by default (on Windows and Linux). The Electrolysis team would love for people to test any plugins on their system, especially less-popular plugins.

Since we are moving relatively quickly with multi-process plugins, there are a few known issues to be aware of:

  • The plugin-crash UI is not finished. The current UI is just a non-localized dialog so that we can get crash reports from nightly testers. This will be changed soon!
  • On Windows, tearing/repainting issues when scrolling, bug 535295
  • On Linux, compiz effects and Flash don’t work together on some systems, bug 535612
  • On Windows, selecting “Print” option in Flash may lock up Firefox, bug 538918
  • On Windows, hulu won’t switch to full-screen mode, bug 539658
  • On Linux with GTK+-2.18 or later, GDK assertions and a fatal XError, bug 540197
  • Firefox-process crashes at NPObjWrapper_NewResolve with silverlight and sometimes Flash, bug 542263

If you discover crashes while running nightlies, please make sure you submit them, and check about:crashes for the crash ID and signature. We could use help making sure plugin-related crashes and instability are filed and tracked by searching for signatures here and filing bugs in the Core:Plug-Ins component.

If your browser hangs, you can probably recover by killing the mozilla-runtime process in the Windows task manager or via `kill` on Linux. If you are a developer with a debugger, please use the Mozilla symbol server and get stacks for both the Firefox process and the mozilla-runtime process and file a bug.

In some cases, it may be useful to the Electrolysis developers if you obtain a plugin log, which is a log of calls made between the plugin and the browser. Instructions for obtaining the log are available here.

I am very excited that we’ve made it this far, and I look forward to our next milestone release, which will backport these changes to the 1.9.2 release in preparation for Firefox Lorentz.

Flash in a separate process

If for some reason you need to disable multi-process plugins, set the pref dom.ipc.plugins.enabled to false.

Error calling method on NPObject!

Monday, January 25th, 2010

When a plugin crashes, content script may still have a reference to JS objects provided by that plugin. The JS objects will throw an exception “Error calling method on NPObject” when any properties or methods are called. Unfortunately, this generic error message is also thrown whenever a plugin method fails for any reason. You can’t tell, just by looking at the exception, whether the process crashed or some other type of failure occurred.

This is important when a test fails: there could be any number of different errors lurking under the surface with similar outward appearance. Today there was a Mochitest error with the following symptoms:

197 ERROR TEST-UNEXPECTED-FAIL | /tests/modules/plugin/test/test_painting.html | [SimpleTest/SimpleTest.js, window.onerror] An error occurred - Error calling method on NPObject! at http://localhost:8888/tests/modules/plugin/test/test_painting.html:105
PROCESS-CRASH | | application crashed (minidump found)
Thread 1 (crashed)
PROCESS-CRASH | | application crashed (minidump found)
Thread 1 (crashed)
PROCESS-CRASH | | application crashed (minidump found)
Thread 1 (crashed)
PROCESS-CRASH | | application crashed (minidump found)
Thread 1 (crashed)

Reading through the log, however, the important output is:

###!!! [RPCChannel][Child][/builds/moz2_slave/mozilla-central-linux/build/ipc/glue/RPCChannel.cpp:276] Assertion (mDeferred.empty() || 1 == mDeferred.size()) failed.  expected mDeferred to have 0 or 1 items, but it has %lu (triggered by rpc)
  local RPC stack size: 2863316886
  remote RPC stack guess: 8
  deferred stack size: 2863316886
  out-of-turn RPC replies stack size: 2863316886
  Pending queue size: 2863317142, front to back:

This assertion is immediately followed by an abort, which is visible in the crash dump output also:

Crash reason:  SIGSEGV
Crash address: 0xbdce4804

Thread 1 (crashed)
 0!mozilla::ipc::RPCChannel::DebugAbort(char const*, int, char const*, char const*, char const*, bool) [ipc_message.h:0235fc257969 : 97 + 0x0]

David B. mistakenly thought that this was a manifestation of Bug 541102 when in fact it is an entirely unrelated bug with similar symptoms. When in doubt about a crash, please check with one of the Electrolysis team to help diagnose and read the log.

Firefox 3.6

Thursday, January 21st, 2010

We released Firefox 3.6 today. If you are currently running Firefox, choose “Check for Updates” from the Help menu. If you aren’t, go get Firefox 3.6 now! One of our most popular new features is Personas, which you can use to style Firefox the way you want. We’ve also made Firefox faster, more responsive, and more secure than ever.

Multi-Process Plugins

Tuesday, December 15th, 2009

Yesterday I landed multi-process plugin support in mozilla-central. By default, this capability is disabled, because there are still some serious bugs. But if you are willing to suffer some temporary instability, we could really use some help testing Minefield nightlies with out-of-process plugins (OOPP).

Currently only Windows and Linux support multi-process plugins: mac support requires additional work. To turn OOPP on, visit about:config, find the pref dom.ipc.plugins.enabled, set it to true, and restart your browser. Please report any crashes or instability in bugzilla: product “Core” component “Plug-Ins”. Where possible, please be as detailed as possible in bug reports:

  • Operating system: please be specific about Windows versions, since Windows XP and Windows Vista deliver some Windows events differently;
  • Page visited;
  • Plugin data from about:plugins;
  • Whether turning IPC off fixes the problem (Note: flipping the pref usually requires restarting the browser to take effect).

There is one major known bug right now: any plugin which is installed in a path with spaces fails to load. On Windows, this affects almost everything except Flash. I hope to have this fixed in tomorrow’s nightly. There is a tracking bug for all the known issues which prevent us from turning on OOPP by default.

Please direct any questions about this work to the discussion list.

Mozilla Status Updates

Tuesday, December 15th, 2009

If you work on Mozilla, how do you coordinate with other people? How do you let people know what you’re working on and ask for help without burdening your coworkers with unwanted email? As part of coordinating the Electrolysis project, I created a webtool which allows people to post status reports in a low-touch way. The Mozilla Status Board allows members of the Mozilla community to post status updates which will be distributed to other people on their teams, and to the public.

A status report is simple: you list items that have been accomplished, what you plan to work on next. Finally, you can list items that other members of your team may need to see, such as review requests, links to posted designs, or even vacation days.

One of the important design considerations was not forcing users into one communication medium. Users group themselves into teams, and each user can decide whether to receive email updates from their team or subscribe to a web feed. For example, if you wanted to see my personal status updates, you can visit my status page or subscribe to my personal feed. And if I wanted to use a feed reader, I could subscribe to the posts of everyone on my team. Hint: to change your email settings, visit the preferences page linked from the header.

Everyone in the Mozilla community is invited to use the status board. In order to keep spammers away, registrations require a password: ask somebody who has already registered, or ask in #developers, or ask any Mozilla employee.

The status board was written in python cherrypy+genshi. The code is hosted at and I am happy to take patches or suggestions. At some point I will probably try to transfer the site from my own server to some Mozilla server, but I’ll make sure that links keep working and data is migrated.

If you’ve been using the status board already, note that I just fixed a bug in the email system: daily/weekly emails were being delivered incorrectly, so starting tonight it should work correctly.

Update: Fixed an issue where Firefox wouldn’t remember your username correctly; renamed “Tags” to “Coordination” to make its intended purpose more obvious, and enabled markdown.