Rated 5 out of 5 stars

Yes, is i try 5.7.5 is work now :) So scroll down if your version is 0.5.7.4 and get this
https://addons.mozilla.org/en-US/firefox/downloads/file/65919/gmail_manager-0.5.7.5-fx+sm.xpi.

This review is for a previous version of the add-on (0.5.7.5).