I fancy myself a fairly technically aware person, and I have no idea what improvements, features or bug fixes Firefox added this quarter that would outweigh all the little and big bad things. In terms of performance, a recent patch made Electrolysis or what it is they called their per-domain process thing the default, immediately making CPU and especially RAM usage shoot up massively (as well as introducing some new bugs pertaining to dead IPC pipes). I tried to put up with it for maybe a week and then switched it off by an about:config switch, which I'm entirely sure they will remove in another 10 versions at the latest. The only way in which I see them adding features takes the form of supporting the latest of the stream of under-the-hood changes that keep coming out of Google's web standard printer, which generally seem to add no user-visible functionality or benefits but are inevitably relied on by some random subset of important websites resulting in the internet gradually breaking if I don't want to update my browser.
I would much rather they use their dwindling influence on standards bodies to block and sabotage the changes that necessitate the constant updating (and attendant maintenance burden which takes smaller browser projects out of the running) at every turn; and if it so happens that this results in their influence disappearing even faster and/or them getting booted, then at least this may pave the way for the long-overdue antitrust suit against Google that many have been saying Mozilla's existence serves to prevent.
(It's not like Firefox is developed by unpaid volunteers. Am I using the browser "for free" if Google sees it as advantageous to pay them money for, among others, my continued existence as a user of the browser?)