Ok I have rebooted and I am in Openbox Bonsai and FF 19. I changed the settings and no difference. Installed Cache Status, cleared the cache and no difference.
It seems like after FireFox 13 things started to get a lot slower for me.
Well if the disk cache is locked at zero, updates are off, search engines
and add-on updates off, it should work OK.
Try private browsing all the time, set it to default.
Copy .mozilla somewhere, delete it in /home/user, and copy it
back. It could be fragmented.
Turn all the add-ons off, especially compact menu !
Reinstall Firefox once, it's worth a try.
Wait 5 minutes and post back.