Ratings...

Highly likely to work well, checked in too.

Probably going to work, probably not checked in.

Big changes, big problems.

Note that these installs need to write to your Mozilla install directory, which means you need to have write access to this directory. If you are on a unixish system and installed your browser via your package management system, you'll need to be root, on Windows™ systems, you might need to be Administrator.