GreaseMonkey installs into Firefox as an extension, see this:
https://support.mozilla.com/en-US/kb/Uninstalling+add-ons#How_to_uninstall_extensions_and_themes

You may also want to remove the GreaseMonkey script folder in the Firefox Profile Folder where GM stores its user scripts.

Other things that need attention.
See http://www.mozilla.com/plugincheck/

Your above posted system details show outdated plugin(s) with known security and stability risks that you should update.

1. Shockwave Flash 10.0 r32
2. Next Generation Java Plug-in 1.6.0_16 for Mozilla browsers

Update the Java plugin to the latest version.

• http://www.oracle.com/technetwork/java/javase/downloads/index.html (Java Platform: Download JRE)

Update the Flash plugin to the latest version.

• http://www.adobe.com/software/flash/about/

"You may also want to remove the GreaseMonkey script folder in the Firefox Profile Folder where GM stores its user scripts. "

"...remove the folder" -- which would be WHERE, exactly??? (it would be nice if you had stated its name and location, since there are about a million sub-sub-sub folders in the Firefox Profile folder)

"You may want to ... " implying that you also may NOT want to... (it would have been helpful if you had told us a reason why we might want to do this, and some possible reasons why it might not be such a good idea to remove the folder)

@jonkers Use the link the-edmeister provided. If you are still having problems Removing greasemonkey, see this:

Cannot Uninstall an Add-on

• https://support.mozilla.com/en-US/kb/Cannot%20uninstall%20an%20add-on

Check and tell if its working.

@jonkers

I am a moderator here, please read the Rules & Guidelines for this forum. If you don't like an answer, just ignore it, or ask for a more complete explanation. No need to be rude to a support volunteer in a thread that you didn't even start yourself.

I have never seen more than 25 folders in the Profile folder and never more than 2 folders deep in those 25 folders - and that was with 85 extensions installed.

The folder is named gm_scripts.

http://kb.mozillazine.org/Profile_folder_-_Firefox