In the past I never had problems with automatic updates, but since the last 2 versions or so I always get a popup informing me that I don't have enough permissions for the update to proceed. I run Firefox as a limited user (under Windows 7), and it's installed in the default location (c:\Program Files - it's the 64bit version). The last version I updated manually, but now I'm getting the update prompts again. I followed the troubleshooting tips on http://kb.mozillazine.org/Software_Update#Software_Update_not_working_properly, and deleted the "update" folder in my profile path, but that didn't change anything.