Unrelated but I just wish they'd stop tinkering with the UI, then trumpeting as if it's a great revolution in web browser UI, when usually it just looks like Chrome from 3 versions ago.
There's no shame in just saying, "you know what, we absolutely nailed it with Firefox 4, so we're just gonna keep that if it's ok with you?". Don't like it? Change the theme or install some addons to add/remove bits.
Also it seems loads of work goes into the integrated developer tools. I ditched Firebug after Australis arrived because it started to take about 10s to load each time. The FF developer tools are pretty good to be fair. But are they actually needed by 90% of users, probably not. In which case they should still be an addon.
The next thing they're going to break in the name of becoming Chrome, is the separate search box. You might need this pref... browser.search.showOneOffButtons
I noticed that a default changed around v32/33 that stopped the DNS suffix being appended to URLs that don't have a domain extension. So if your users find that typing support or intranet into the URL bar ("awesome bar" apparently) thinking that they are going to a web address when it actually ends up googling for it, then you'll need this pref... keyword.enabled;false
I've built up quite a library of these preferences and addons since it started becoming Chrome. Still miles better than Chrome though for power users IMO.