Last month, I started to find that Firefox was not as responsive as it used to be on Snoopy, my main workstation.

And last week end, I decided to completely refresh my firefox profile. With the help of this article [mozillazine], i moved only what i could not afford to lose, such as my bookmarks (bookmarks.html) and my saved passwords (key3.db and signons.txt). After that came the time to (re)install firefox extensions. I didn't reinstall Tabbrowser Preferences in favor of Tab mix plus, which is more configurable and generally more advanced.
But googlebar and all-in-one sidebar both passed the refresh test, and i now have a very responsive firefox back.