Comment 0 for bug 1485741

When Mozilla initially switched to Yahoo by default for US users, it did this with a geo-specific preference (browser.search.defaultenginename.US), used when the locale was en-US, the user was in a US timezone and Firefox was not a partner build. This meant that Ubuntu builds continued with Google as the default search engine.

Some users are reporting that the default is switching to Yahoo after upgrading to 40.0, which is not intentional.

Since http://hg.mozilla.org/releases/mozilla-release/rev/37ea9e22ac42, it looks like Firefox downloads a region specific default from a Mozilla server even for partner builds like ours.