address bar suddenly stopped working, & now navigation buttons are gone

Right click at the top of the screen, just below the title bar (for example, to the right of the Help menu), and click Customize...

Now you can restore your interface to being however your like it.

As for your home page, go to Edit > Preferences, and click General at the upper-left corner of the window that comes up. Your homepage is probably "about:blank" right now; change it to whatever website you want as the default.

If you don't like that method, or it doesn't work, then you should be able to restore your interface and home page to the default along with the rest of your profile by making sure that Firefox is not running, and then opening up a Terminal window (Applications > Accessories > Terminal) and running the command:

mv ~/.mozilla ~/.mozilla-broken

(To run a command, type or paste the text into the Terminal, and press enter.)

If that command produces no output, then it succeeded. Run Firefox again, and it should be just like you've never run it before. Note that if you use this method, you'll also lose browsing history, cookies, saved passwords, bookmarks, and so forth.

If you use this method and are happy with the results, then you can delete the old, broken profile. However, doing so is entirely optional. If you wish to do so, run the command:

rm -rf ~/.mozilla-broken

That command will produce no output even if it fails, so to check if it fails, you can run the command:

ls -ld ~/.mozilla-broken

A message like "ls: cannot access /home/username/.mozilla-broken: No such file or directory" means that you successfully removed the old broken profile.

(By the way, unless you have a specific reason to be running firefox-3.0, you're probably better off running the latest stable version of firefox provided by Ubuntu, available through the plain "firefox" package. This is currently the Firefox 3.6 series, and it's present by default on all currently supported versions of Ubuntu Desktop Edition and Ubuntu Netbook Edition. Or perhaps you really are using Firefox 3.6, and the indication of "firefox-3.0" as the package affected by this question is incorrect.)

yes it's firefox 3.6

I tried the method specified above, all it did was say 'try mv help'

p.s. I made the mistake of following instructions elsewhere, to right-click, & now file/edit/view/etc are gone too.......

If you got "try mv help" it sounds like you didn't enter the commands correctly into the Terminal. Make sure to enter them exactly. You can copy and paste them.

If you still experience this problem, then after attempting the instructions in the Terminal, please select all the text in the Terminal and paste it here.