firefox not shutting down

Please open a Terminal window and run this command, by copying it from here, pasting it into the Terminal, and pressing enter:

lsb_release -a; apt-cache policy firefox; which -a firefox

Then select all the text in the Terminal (Edit > Select All), copy it to the clipboard (Edit > Copy), and paste it here.

Please also check whether or not this happens when you run Firefox after logging in to your Ubuntu system with a different user account. If you only have one user account, you can create a second account to test this. I am not suggesting that you should start using a different user account if this works; the purpose of this is to narrow down the cause of the problem. (If the problem does not occur with the other user account, then the cause is probably in your user-specific Firefox configuration, though a bug may also be involved.)

Today is the last day of your life so far.
steve@steve-desktop:~$ lsb_release -a; apt-cache policy firefox; which -a firefox
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 10.04.3 LTS
Release: 10.04
Codename: lucid
firefox:
  Installed: 3.6.18+build2+nobinonly-0ubuntu0.10.04.2
  Candidate: 3.6.18+build2+nobinonly-0ubuntu0.10.04.2
  Version table:
 *** 3.6.18+build2+nobinonly-0ubuntu0.10.04.2 0
        500 http://gb.archive.ubuntu.com/ubuntu/ lucid-updates/main Packages
        500 http://security.ubuntu.com/ubuntu/ lucid-security/main Packages
        100 /var/lib/dpkg/status
     3.6.3+nobinonly-0ubuntu4 0
        500 http://gb.archive.ubuntu.com/ubuntu/ lucid/main Packages
/usr/bin/firefox
steve@steve-desktop:~$

still happens with other user account.

That is strange; usually this sort of problem does not happen when running Firefox in a separate user account. I wonder if perhaps it is caused by one or more malfunctioning add-ons.

In Firefox, please go into Tools > Add-ons, maximize the window if it is not already maximized, take screenshots of the screens showing your Extensions and your Plugins (you can take a screenshot by tapping the Print Screen key once), make sure everything is visible in the screenshots, then post them on the web (you could use a site like http://postimage.org) and post a link here to the screenshots.

here are the screenshots-
http://postimage.org/image/1my6vq3s4/
http://postimage.org/image/1myyzv06c/

Do you use thunderbird for email? If not then run:

mv ~/.mozilla ~/.mozilla_old

Then try the browser, is it ok?

yes I use thunderbird

ok then use:

mv ~/.mozilla/firefox ~/.mozilla/firefox_old

ok, done that and is shutting down ok now, will test for 24 hours and if still ok will mark as solved.
thank you Eliah and Andrew for your help, much appreciated.

didn't work, still doing the same.

Thanks Andrew, that seems to have done the trick.

Thanks actionparsnip, that solved my question.