I too went to HELP --> UPDATE and it came down and installed, never did that before.
Also, I'm on a 64 bit W7, and I previously had ALWAYS gotten an install failure that I recall it couldn't install for some reason or other. On my desktop I have many single URL icon's, and it never would work with these (close FF, re-open, and the install should complete). I had to use a REAL FF icon, and I had to run it as Administrator to make it correctly install. Yesterday when I used a URL icon it installed with no problem? Odd... but something has had to have changed? Now that I think of it, my wife's system which is also W7 x64, let me check...
That FF is also set for Automatic Update, and the minute I opened ABOUT it started checking for update, d/l'ed it, and installed it. Button to re-start FF and install. This was on a URL FF icon too. Re-started to FF 16.0.1 without problem? Something surely has changed from prior versions.