Rated 5 out of 5 stars

It works fine in 4.0. The xpi file simply needs to be updated to show that.

You can force it to enable using http://www.mrtech.com/extensions/#toolkit .

Options > Miscellaneous > XPI Install Options > Uncheck "Enable Addons Compatibility Checking"

Then restart Firefox.

This review is for a previous version of the add-on (1.2.1-signed.1-signed).  This user has other reviews of this add-on.