Lets start with what is your processor, and memory. How long has it been going on? If you hardware is really old, and you're trying to use the latest Firefox on a decade old computer with a limited amount of memory it can cause it to be slow to respond. If you have at least a dual core processor, and at least 2GB of ram you're probably fine in that department.
Another easy check would be to run Firefox in safe mode, or turn off the hardware acceleration to see if that's part of the problem.
»support.mozilla.org/en-US/kb/tro ··· r=1&as=s
In more extreme cases with all the changes they made to profiles it's easy to make a new profile, and if it's not a problem on the new profile the old profile is corrupt. In my opinion the changes over the many versions, and additions extensions can make can cause problems with the profile. It's suggested you leave your old profile alone, and just see if the new profile responds better, even start re-adding in the extension in one by one to see if they start causing the undesirable behavior.
»support.mozilla.org/en-US/kb/pro ··· profiles--
I distrust those people who know so well what god wants them to do because I notice it always coincides with their own desires- Susan B. Anthony
Yesterday we obeyed kings, and bent our necks before emperors. But today we kneel only to the truth- Kahlil G.