Recently a forum member over at Go Firefox! was getting the below error whenever they tried to install a GreaseMonkey Script. They recently reinstalled Firefox with a fresh profile. They could install GreaseMonkey without issue but any time they tried to load up a script they got this ugly error:

Now, I know I had seen that error before but still took some searching to find the solution. Turns out this is caused by either a missing or damaged GreaseMonkey folder inside the profile folder. The fix is fairly simple and should only take a couple minutes:

1. Locate Firefox Profile Folder.
2. Check to see if there is sub folder called gm_scripts chances are it won’t be there. If it is missing go ahead and create it. In Windows Explorer go to File >> New >> Folder.  This will create a folder called New Folder, rename this to gm_scripts. Continue to next step
3. Check this folder to see if there is a config.xml file. If not, in Windows Explorer go to File >> New >> Text Document. This will create a 0 KB text file called New Text Document.txt , rename this to config.xml

Note: If you have not previously installed any GreaseMonkey scripts and the gm_scripts folder is present with files and folders inside of it, delete the contents inside the gm_scripts folder and then recreate the config.xml file as described in step 3.