Mozilla’s rollout of Yahoo! as default search engine (a.k.a. What’s up with Firefox 34.0.5?)

Two months ago Mozilla announced the big news: the default search engine in United States will be Yahoo! rather than Google. The change should be introduced in Firefox 34 but rolled out gradually after the release. That announcement already made me scratch my head and wonder how that rollout would actually work — not enough to go figure out the details however.

Recently however I saw this blog post claiming that the Yahoo! market share on Firefox 34 in the US increased by factor 3 compared to the previous Firefox release — already on December 2, a day after the release. Quite impressive, but how is that even possible if the rollout was supposed to be gradual?

So I decided to look into how Mozilla did it. Release notes link to a complete list of bugs fixed (yes, 3778 of them), and a quick search shows that bug 1102416 is the relevant one. Some interesting details there (in particular, “United States” is currently defined as “en-US locale and timezone between Newfoundland Daylight Time and Hawaii-Aleutian Standard Time”) but not much on the rollout approach.

Wait, what is Firefox 34.0.5 that this was pushed to? I have Firefox 34.0 installed and no updates are available. Looking around, I don’t seem to have code from bug 1102416 in my browser either. A web search later I finally got it: Firefox 34.0.5 is the release changing default search engine in the US, and it was released in parallel to Firefox 34.0. So the gradual rollout worked by gradually rolling out Firefox 34.0.5.

Ok, so how fast was it rolled out? The application statistics shown by Addons.Mozilla.Org cut off minor revisions unfortunately, so distinguishing between Firefox 34.0 and 34.0.5 isn’t possible. Statistics generated from Adblock Plus server logs show the full picture however. During the first week after the release Firefox 34.0 reached 15-20% of the entire user base, whereas Firefox 34.0.5 was indeed being rolled out very slowly, only getting to around 2%. And everybody else? Well, they kept using Firefox 33.1.

On December 8 somebody at Mozilla flipped the switch and now all the sudden everybody was updating to Firefox 34.0.5 — with the exception of the people already using Firefox 34.0. By December 15 the state stabilized and the Firefox user base was divided into people using Firefox 34.0 and the ones using Firefox 34.0.5. I guess that the Firefox 35 release (scheduled for tomorrow) will bring everybody back on the same Firefox version.

It seems that after years of boring releases every six weeks we are in for some variety in the Firefox release cycle now. Oh, and what about StatCounter seeing so many Firefox users switch to Yahoo! overnight? Merely a fluctuation, it seems…


  • Tyler

    34.0.5 was initially only for new downloads from, it wasn’t deployed to any updates for sometime. After it was proven to be stable it was deployed as an update to all users under 34.