I think it's a fantastic feature and I have [intentionally] used it loads of times.
Granted, there is the rare (0.1% unscientifically tested) occasion where I'll go back inadvertently but FF remembers what you had typed in most cases (it is partly, I think, down to the design of the web page though). What would be a good thing that might solve the problem for those less, ummm, loving of the feature would be a simple tick-box in the options to turn it off!
That and the way that Firefox thinks it clever to get you to search in the address bar, when you've specifically clicked in Google's search box. Grrr. That's one less FireFox user. Hello Chrome!
??? I've never had it try searching in the address bar when I've clicked in the Yahoo (I've changed mine) search box... What have you done to it?!? I've used the Beta and occasional A_lph_a (not a swear word in this context :P) releases only with main releases over the last few years (been with FF since about v2 or 3 I think). I just didn't like the Chrome interface last time I saw it and haven't seen any need to switch. Each to their own I guess.