Rated 5 out of 5 stars
I am waiting to upgrade to FF5.x until this extension works with it. Is it working for anyone who manually increased the maxVersion?
A simpler way to increase maxVersion:
1) Download 7-Zip from http://www.7-zip.org/
2) Open the XPI file with the 7-Zip file manager
3) Right-click on install.rdf
4) Choose Edit
5) Make the changes suggested by e9571186 below.
6) Close the editor and save the changes, which updates the archive too.