I don't think that I have any problems with Fx17 at all. It's not about Fx not working on 64-bit Windows, Mozilla halted development of Win64 builds of Firefox until further notice due to most likely incompatible plug-ins that don't work correctly in 64-bit browsers.
I LOVE Firefox 17.0.1. Appearence-wise, it hasn't changed, but performance-wise, oh yes. It's actually not as slow as Firefox 16 was (Kept not responding and kept slowing down at times), so I really have to applaud the creators for speeding it up!!!!!
I reluctantly updated today, from Firefox 15 to 17.01... reluctantly, because of the dumb change with the tab-bar and the lost of my favorite ''theme'' (incompatible with v.17)... and now, I seem to be facing a weird bug that I can't solve OR find information about.
So... I found a new theme for Firefox 17, installed it and restarted Firefox. Marvellous, it works fine.
Then, I close Firefox (to do something for a few minutes), reopen it, and... my ''theme'' is reseted to 'Default' AND my 'TACO' addon is deactivated even though it's compatible (If I click to update it, it say ''ready to update'', restart Firefox, work fine (even though the version doesn't change)... then is ALSO reseted to 'Deactivated' if I close/reopen Firefox).
It's rather annoying... and could be problematic to me.