Nope! I checked that too. The only login item is Stickies and that app won't let me delete lines on it. And why would FF auto-install in the Dock every time? My desktop is in some kind of "Groundhog Day" scenario if you get the reference to the old Bill Murray movie. I'd hate to go through the effort but I'm tempted to wipe my HD and reinstall Lion. I've already reinstalled the OS but not that major.
Well, it was worth checking, since you didn't say you'd checked login items.
Other questions, then:
Does it open a specific URL, or just your home page (or blank)?
If Firefox set as your default browser? If you change to a different default browser such as Safari, does Firefox continue to open? or does Safari?
Those will help pinpoint the source - whether it's Firefox itself, or just a URL that's indirectly launching Firefox.
One of the first things I checked. Firefox is not set to open on login.
Interesting thought and something that I hadn't tried. Unfortunately, FF still opened after setting Safari as default browser. Then, when I went back to Safari to reset FF as default, Safari was no longer my default. It had set it back to FF.
The other question is, why can't I delete a text line on a Stickie note. Even if I delete the note and type a new one with the same text, the deleted text reappears at startup. I deleted Stickies from my Login Items but it opened again at startup and reinstalled itself as a Login Item.
This all started when I couldn't delete desktop items without it asking for my password. I tried all the permissions tricks to fix it but nothing worked so I reloaded Lion. That fixed it but caused these other problems.
My guess is it's a corrupt user account but how do I fix User Account prefs without creating a new user and deleting my old one?