Firefox nexer versions keeps making my mouse hang and keep crashing. same settings on v4 is worling great.

Question

Ok so it started few days ago( when v 15 was new version),
1) firefox lasted at max a minute before crash saying firefox encountered unspecified error and will exit. Then the send crash report box would open.
2) When it was working; my muse kept hanging, like if you unplug it and then plug it in, no problem on other browsers with same sites but on fox it did.
Remedial steps taken:
1) I disabled all addons and extensions no dice.
2) re installed it using v 15 then 16 beta then 16 today no dice
3) Re installed windows and installed Firefox works fine but when i import my stuff from backup even without addons and extensions (using mozbackup) it starts the problems again. repeated step 2 but still zip.
I uninstall it and install version 4. import ALL settings even plugins extensions addons everything and it is working like a charm.
why on earth does newer versions have a problem with it.? they are supposed to be more resistant to crashes.

Answer 1

Turns out it was a problem with "general setting".
i installed v 16.0.1 and then restored from previous profile things one by one.
and at last when i imported general settings it caused problems.
so i left that out and now it is working awesome.
i had moved the positions of icons in toolbars and probably thats why when newer version is installed it cannot make sense of it and starts doingproblems(well thats my guess).