> For most FF is very responsive and there are no problems what so ever.

Open dev tools, type `for (;;) {}`. Notice the whole browser becomes unresponsive. This has been improved upon (as in it doesn't block the whole Firefox UI, just merely every single content tab) thanks to Electrolysis partially reaching stable but "there are no problems whatsoever" simply isn't true performance wise (and this is the most obvious one, there are numerous other very well known performance issues with FF)