I'm using firefox for several years, but recently i discovered a weird effect on one of my computers, which was consistent across many FF versions (up to the recent version 17 now).
All drop down menus on facebook were not working for me. On one pc I can click on the red globe, and a menu opens - while on the other pc nothing happened. Now I was able to reproduce it.
As soon as I activate the "ask how long cookies are stored" option in the privacy settings, the drop down menus wont work/show. Choosing the default "Keep them as long as they are valid" reenables the drop down menus.
I really like the cookie storage time option so i can decide which website will remember me.
This works. I had www.facebook.com and pixel.facebook.com allowed and no other request appeared. I would guess that pixel and www wanted to access the same cookies but the cookie handling in FF blocked that "cross url" cookie access.
I have been having this same problem too. I've tried disabling all my add-ons/plugins, but it hasn't helped. I added back just Java, but that did not help. I have also added an exception for facebook and pixel.facebook.com, no dice. It does work correctly in my IE.
I have also run malware scans (GMER), nothing shows up. If I set it back to remember history, removing the custom options, it works.
I just wish I had found this thread earlier - I just spent a day trying to figure this out (including resetting and re-installing Firefox) only to find that it worked for a few minutes and then broke again. Doh.