Tim:
I shall ask the obvious question: Did you completely quit Firefox so that there were no other running Firefox processes?
Andre Robatino:
You're right, that must have been the problem. Last night I noticed that there was a running Firefox process even after quitting the graphical Firefox window, and killed it. This morning, Firefox gave me the message about having trouble restoring the previous session, so I just started a new session. Add-ons/Extensions now shows the correct version, 2.6.6. Sorry for the noise.
That's okay, I've been burnt by that one, before. Particularly during yum updates. Other software seems to handle being updated, while it's still running, usually quite okay. You carry on using the old version from memory, until you quit. Then the next time you load the program it's the new version. Firefox, on the other hand, would often jam up on me when updated while in use, and needing quitting and restarting.