Web browser resets to Safari

[Grga]

I have been using Firefox as my primary browser for some time now, but after a Software Update a few weeks ago (I think it was one of the QuickTime security patches), my system started resetting my browser to Safari after I reboot. (Oddly enough, this doesn't happen after every reboot, but probably 9 times out of 10.) My E-mail client also keeps getting reset from Thunderbird to Mail, but that's less annoying, because I rarely click on mailto: links.

I have been told to go into Safari (and Mail) to change the settings, but they keep changing back after rebooting.