How to sync GreaseMonkey scripts between computers?

I use Dropbox to sync greasemonkey scripts:

1. Make a folder: My Dropbox\App Sync\Firefox\
2. Find your profile directory ([random string] wil be something like 2b5dk3bs)
   • XP: C:\Documents and Settings\[username]\Application Data\Mozilla\Firefox\Profiles\[random string].default
   • Vista: C:\Users\[username]\AppData\Roaming\Mozilla\Firefox\Profiles\[random string].default
3. Move the gm_scripts folder to My Dropbox\App Sync\Firefox\
4. Use the Link Shell Extension to create a Junction called gm_scripts in the profile directory. A Junction is kind of like a symbolic link. To do this, right-click the gm_scripts folder in your Dropbox and click 'Pick Link Source'. Then, in your profile directory, right-click and pick Drop As >> Junction.
5. For every other machine, delete the gm_scripts folder in your profile, and add the junction as before.

I also use this trick for extensions, mouse gestures redox config, stylish, and menu editor files.

Since Greasemonkey's December 2013 1.13 release there is an option to use Firefox Sync to keep installed User Scripts the same on all your browsers.

See also a September 2013 blog post: Firefox Sync coming to Greasemonkey.