I've been saying this ever since they changed from releasing those .# updates, aka after Firefox 4.
There was NOTHING wrong with releasing Firefox 4.1, 4.2, or even 4.2.3. We were all used to it. Firefox 3.6 hit 3.6.28 before Mozilla stopped supporting it.
That, coupled with the overbearing UI changes essentially made me stay at version 3.6 until I couldn't take the lack of new internet standards, like HTML5, which happened to be about a week before Mozilla would force update everyone using 3.6 to version 12 (if they had auto updates enabled).
I went through days of research and troubleshooting trying to get Firefox 4+'s UI the same as 3.6, and after tweaking options, installing a menu editing addon and finding Stylish scripts, I managed it.(although the addons page is still the new dumbed down one, the general UI while I'm normally using the browser is enough like 3.6 to be comfortable using 12. Yes, including the stupid tab groups link on the 'list all tabs' button AND the delayed tab sliding when closing one, which was ripped right from Chrome by a suggestion Mozilla listened to. Those two things alone caused me immense trouble trying to navigate my tabs.)
Couple these issues with the widely known flash issues we're having, and Firefox really took a step down in a hard way. (I started having pink screen lockups after upgrading to Firefox 12. On 3.6 my display driver would crash, never lock up my system. Eventually fixed in the 11.3 flash update, which then introduced the freezing issue.. which appears to be fixed now, but with the latest update I'm now experiencing desync when watching flash videos!)
I've tried Chrome and I hate it because of how uncustomizable it is, but I keep it installed in the off chance Firefox doesn't work properly somewhere (or I want a whole new session for something on a relatively speedy browser, despite it opening tons of processess and using a lot of memory, the latter Firefox is notorious for).
So yes, Mozilla shot themselves in the foot by changing their focus like EVERY company seems to have been doing as of late..