I had this issue when I updated my version of firefox to 5.

Quite frustrating, especially when it renders your internet browser practically useless.

I fixed it by right clicking on the top menu bar and left clicking customize.

When the 'Customize Toolbar' appears, left click on 'Restore Default Set'.

Fixed it right away.

Hope this helps :)

Mozilla Firefox, the browser, and your profile (contains all of the data, like bookmarks & passwords) are in 2 separate locations.

1. Program Directory
2. Firefox Profiles - Where Firefox stores your bookmarks, passwords and other user data

Before running a Firefox Update, which updates your Program Files Mozilla Firefox, the least that you can do is, Clearing private data << as to try and make the old profile as compatible as it can be with the new version of Firefox that you're upgrading (updating) to.

If you haven't done this, or whatever happened, for example there are incompatible add-ons - or the whole thing went berserk, like for the OP twilightsmith, then the easiest thing that you can do is run Firefox in Diagnose Firefox issues using Troubleshoot Mode.

Check out the links and also the screenshots posted, add-ons can be permanently disabled from the Safe Mode start-up dialog - so you don't have to mess with your profile if it's something more severe than the address bar not showing up.

Hope it helps!..:)

ps. I keep posting the same thing everywhere, since there are no signatures possible on this forum. :( To allow installation of older, or incompatible add-ons, use https://addons.mozilla.org/en-US/firefox/addon/add-on-compatibility-reporter/ and/or the Nightly Tester Tools add-on (but the linked 1 is from Mozilla).