Originally Posted by
SgtBrutalisk
Yes, I am using administrator rights.
I've discovered what was going on.
Because I got error messages that were mentioning something about proxies, I got an idea to check Firefox 3.6 options and found the following:
When I go to Tools>Options>Advanced>Network>(Connection) Settings
there is a choice of four radio buttons:
1) No proxy
2) Auto-detect proxy settings for this network
3) Use system proxy settings
4) Manual proxy settings...
In my case, option number 3 was selected.
I am quite sure I've never messed with those settings and I'm confident the only time I was curious enough to check them option number 1 was selected.
Switching it to number 2 made Firefox 3.6 work again, although with certain visual glitches on websites - Facebook wouldn't display all its icons properly, but otherwise it was usable.
Switching to option 1, "No proxy", made everything normal.
Conclusion: Somehow, Spybot - Search&Destroy changed Firefox's proxy option. I have no knowledge on how this might have happened, but I did use "Undo immunization" while Firefox was running.