firefox issues

[Spidey]

i seem to not be able to install *any* firefox extensions, or update the ones i have (stumbleupon and adblock).

every time i try to do so, it tells me that firefox is set so that things can't be installed, and tells me to change it. so i do. but when i do, i get the same error over and over and over again and it's getting quite. old.

i'd really like to update my extensions and install some new ones. anyone know what to do? not being able to install or update extensions is becoming a big pain in the butt.

i have the newest version of firefox for the mac.