This article helped me today to upgrade to latest firefox.

Somehow, I messed up with firefox installation in Mint and could not figure out. I installed another firefox and uninstalled it, tried several tricks by Google but none worked.

Finally I searched randomly on firefox and it really helped. Thought this is described for firefox-4 but it works for firefox-8 as well as what I did.

So, I am sharing this

http://support.mozilla.com/en-US/questions/795196