For a few years now when i open firefox, theres a message saying "firefox already running and not responding".
It works ok otherwise so I let it be.

Recently, the google, yahoo,,, search bar stopped working at times.

I tried disabling all add-ons.

There are 2 add ons I cannot disable which are Morning coffee and No-Script

Any clues

One of the thing that can cause this is a lock file corpse hanging around (if, say, at some time or other the system crashed, Firefox crashed, who know what).

First off, exit Firefox either with the File drop-down Quit or simply click the X at the top right corner of the screen. Then, in your home directory,
If that file exists (it shouldn't when Firefox is not running, it's a corpse and you can delete it. If it does not exist, then you should be all right but there are other places to have a look-see.

You should be running version 3.6.13 (the current stable version); if you're not, update to the current version from your distribution software updates. Also, in the Tools drop-down Add-ons and check for updates (there have been a couple recently for Adblock Plus and NoScript). I doubt those are causing any problems, however.

Finally, are you by chance double-clicking to start Firefox? Just a thought.

Hope this helps some.