In order to uninstall a possibly unwanted extension, please do the following:

1. From the Firefox window click the Firefox button at the top left and select Add-ons, or, if the Firefox button is not shown, click the Tools menu and click Add-ons.
2. Once the Add-on Manager has opened in a new tab, click the Extensions button on the left side of the window.
3. You should now see a list of your installed extensions on the right side together with buttons on the right side of each extension.
4. To remove an extension from Firefox, simply click the Remove button. You should see a message that informs you about the successful removal of the add-on.
5. Note that some add-ons require a Firefox restart to be removed completely. To perform a Firefox restart after the add-on removal, click the Restart now link in the message.

You can find further information about uninstalling extensions in the following articles:

Disable or remove Add-ons

Remove a toolbar that has taken over your Firefox search or home page

Sounds like some form of ad-aware.

Boot up your pc in safe mode w/ networking, open FF and type "about:plugins" in the url address bar. Take note of anything that looks like it may be associated w/ "Facemooch". Close FF and do a search for any malicious looking files listed under the plugin section and append "bak" to the extension. You may need to open task manager prior to doing this to ensure the file isn't running, if "rundll32.exe or a malicious looking file, a simple search should be able to determine this, end the task prior to changing the extension (ie. somefile.dll.bak) <- this can be changed in the search wizard.

Fire up msconfig while your still in Safe Mode, and uncheck any startup programs that are of unknown origin. (this does not delete anything, but just keeps it from booting at startup) msconfig should be available from the run command, just type in "msconfig" and enter.

norton also has a freeware program called "autorun", very useful in stopping malicious files in their tracks.

Most file validity can usually be determined by the directory they are lying in, for example, most viruses or malicious programs tend to load themselves into the c://windows/system32 directory or root directory (synonym).

A quick google search also revealed this: http://www.howtogeek.com/forum/topic/how-do-i-get-rid-of-face-smooch