Firefox always re-selects the entire URL in the address bar when I go away and then return to the Firefox window and that’s always annoyed me. Now, courtesy of lifehacker I’ve reset that behavior. How? From the Address bar, enter “about:config” (sans quotes). Locate browser.urlbar.clickSelectsAll and change its value to false.
And, while I’m at it, here are a couple of other things I’ve found:
Firefox extension Stop Autoplay.
Two Adobe Reader replacements: Sumatra and Foxit. Sumatra has a very small footprint but Foxit is more complete.