With all the brou-ha-ha about firefox 25, and all the unfortunate changes that were supposedly coming, I wasn't sure what to think. So I snagged a copy to play around with, before updating all my devices.
Basically... I can't tell that anything changed. Certainly nothing I care about, that I can see so far. I haven't started a new profile yet, but I think many of the changes I'd already be patching around with other addons anyways.
When I first opened my old profile, I couldn't use the address bar. At all. Disabling the Omnibar and Background Tabs addons let it work again, and it still works after re-enabaling Omnibar. I don't know if "just" disabling Background Tabs would have done the trick.
All my other addons seem to be working. One of them is evidently stopping the 'hide forward button' so-called feature, I wish I knew which. I _hate_ that 'feature'. Maybe it's a setting somewhere in about:config instead.
The 'magic' stop/reload button behavior is still in evidence.
As far as I can tell, new toolbars are still an option. I haven't tried anything even more exotic yet.
The addons 'Tree-Style Tabs' and 'Vertical Toolbar' still work fine, so far as I can see.