Or get really crazy and find yourself a halfway decent text editor like Notepad ++ and do a search-and-replace in the folder
C:\Users\((your user name))\AppData\Roaming\Mozilla\Firefox\Profiles\((some string)).default\gm_scripts
and all included folders, which will take like 10 seconds
C:\Users\((your user name))\AppData\Roaming\Mozilla\Firefox\Profiles\((some string)).default\gm_scripts
and all included folders, which will take like 10 seconds