Greasemonkey to Firefox add-on converter: why bother?
But what if you want to install all those userscripts as separate add-ons? Well, there's a userscript-to-xpi converter that – Wait a minute.
Why the heck would you want to install your userscripts that way? Loading up Greasemonkey is a lot faster than individually converting your scripts, and it also gives you access to any preferences that might come with them. Converting them to extensions seems like it would bog down your add-ons list, on top of being a royal pain the butt.
If you still want to go through with it, for some reason, the converter is an easy web form and seems to work pretty well.