It’s a symbolic link. I tried moving the actual .mozilla back into ~, but it made no difference (i.e. the Install link still wouldn’t work). FWIW, when ran from a terminal, Firefox prints

shouldload: http://userscripts.org/scripts/source/31864.user.js"
ignorescript: false

when I click the Install link with autoHideStatusbar running. It’s the same it does when autoHideStatusbar is disabled, but with the latter, it also prints ”ignoring next script…” and then the installation pop-up appears as it should.

Don’t worry too much about fixing this, I install scripts rarely enough that working around this by disabling autoHideStatusbar each time isn’t too much of a hassle. Although of course, if a solution is found, I’m all the happier.

(And I’m sorry, ky_bluegrass, for hijacking your thread.)