Text editors

My experience for Firefox PR:

You CAN edit user.js in a text editor
You have to restart Firefox TWO TIMES for the changes to take effect, at least when FF is open during editting.

The urls divided by spaces DOES work, I used without www.
Ctrl-V does work, at least for moodle implementations (i.e. this forum and my own moodle), but for some strange reason not in the mentioned mozilla demo at mozilla.org, when entering multiple sites in the settings (at least, I think it worked when just with mozilla.org, when adding moodle.org and my own domain, the moodle things still worked with ctrl-v, the mozilla.org one didn't. Weird)
For subdomains (i.e. something.bbb.com), adding bbb.com is not sufficient, add url including subdomain (http://something.bbb.com)

I hope this is somewhat helpful, I got very frustrated because the dividing by spaces didn't seem to work and sometimes even one site didn't, then through coincedence I got the idea you might have to restart the whole thing twice and it worked fine. Again, editting with a text editor (of user.js that is) works fine for me, I restarted a bunch of times now and the settings still work like they're supposed to).