Ubuntu Firefox it is saying that it is already running but not responding

It's probably that your profile is locked; happens on unclean shutdown sometimes.

See this support page on Mozilla.com, specifically:

• pkill firefox (or restart your computer). Don't try to start Firefox.
• Go to your Firefox profile folder - see How to find your profile.
• Delete the lock file parent.lock

Your profile is in ~/.mozilla/firefox/*.default/ (the * will be a random sequence of 8 letters)

rm parent.lock and try again.

Open terminal window. type:

sudo killall firefox

Try to open firefox again

This post could be the solution @ http://ubuntuforums.org/archive/index.php/t-493848.html

If you need to kill firefox, you can try going under System->Adminstration->System Monitor and select the processes tab. Look for firefox and right click on it. It should give you an option to kill the process. If that does not work, you might try going into the Terminal and type:
ps -ef|grep firefox

If firefox is running, it should show up as a process and have a number attached to it. It will be the first number after the username. For example:

jayhawk@jayhawk:/$ ps -ef|grep firefox
jayhawk 8137 26283 0 14:21 pts/0 00:00:00 grep firefox
jayhawk 24213 1 0 07:22 ? 00:00:00 /bin/sh /usr/bin/firefox-granparadiso

In this scenario, the process number is 24213 for firefox (I am running the alpha version of firefox so your firefox name will be different). Just type:
kill 24213

Then check again by using the ps -ef grep firefox command. If it is still there, you can use:
sudo kill -9 24213

And that should kill it.