As for Firefox, on this laptop (my main one) I am still using Firefox 3.something. And, yes, I have problems with it. Sometimes it refuses to load, so I just go to Chrome for that day which has all my imported tabs and bookmarks from Firefox. That makes Firefox sit up and take notice, and it usually behaves for the next few days.
My daughter's baby laptop is running Firefox 9 but I suspect that I should have left it at Firefox 3. something too as it only has minimal 512mb ram and can't be upgraded (because the ram is netbook ram, hundreds of dollars to upgrade here, better to buy a new laptop.) So, it takes absolutely forever to load. (I'm talking 9 minutes from turning it on to having Firefox ready to go with 3 tabs maximum).
So, I don't think I will be going to Firefox 10 any time soon, although my main laptop has 1.5gb. Both laptops run XP Pro. I am intending to purchase a new laptop later this year when I have saved enough money, probably by then it will be Windows 8 and Firefox 15, lol.