I just got a window on my screen saying, "Firefox has downloaded an important update and must restart". I clicked on OK, and FF happily shuts down, starts up and says, "Firefox is installing updates and will start up in a few moments." And it did.
I was running Firefox 1.5 RC2 and the update, I suppose, was the release version of Firefox 1.5. After a hell of a long time and a ton of complaints, Mozilla have finally implemented the patch mechanism.
Looks like they got it right!