Success Story

The system is working. We found a crash bug soon after it was introduced, and saved Firefox users pain and aggravation.

Yesterday, dbaron was looking through data from and found a spike in crashes on nightly builds. Because this was a bug related to delivering stream data to plugins, an area that I rewrote for Firefox 4, dbaron cc’ed me as he filed bug 646839.

The bug immediately triggered alarm bells for me: all of the crash stacks were taking “unusual” paths having to do with multipart streams, or networking code that was being intercepted by JavaScript, probably from an extension. In addition, nothing had changed in the Mozilla code that looked remotely related to the crash. After some data mining, I discovered that the users who were crashing had a beta version of Adblock Plus installed. I immediately cc’ed Wladimir Palant, the ABP maintainer.

It turns out that a new feature in Adblock Plus was eating some error codes, leaving our plugin code in a bad state. This resulted in crashes. And the new version of Adblock Plus was schedule for release to Firefox release users soon! Because of dbaron’s quick discovery, a nightly user base who runs beta versions of extensions, and quick thinking all around, we were able to avert a problem for users of Firefox release builds.

This kind of success story is possible because of many tools and systems which interact, but it is mostly possible because Firefox development is an open community where everyone works together and we don’t hide our flaws. And that’s why I love working on Firefox.

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Atom Feed for Comments 2 Responses to “Success Story”

  1. Wladimir Palant Says:

    Only a small correction: this Adblock Plus build wasn’t only used by Firefox nightly users, but it didn’t crash in Firefox 4 for some reason. Fortunately, with 5000 Adblock Plus nightly users we still got a significant intersection.

  2. Mook Says:

    Sounds great!

    Would the problem of getting into that state still be fixed? Adblock, while popular, isn’t the only extension that might want a listener there, and somebody else might have the same bug. Especially with the error console spam as mentioned in comment 11, I suspect people will want to catch it…

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