Works really well, should have compatibility Rated 4 out of 5 stars
This addon works very well for displaying quick information about your ISP's net usage!
If you are able to understand how it parses the webpages, you can even add a new ISP to the list.
The one drawback is that the author doesn't submit the newest versions to AMO, forcing people to go to an external website and get a version which has not been reviewed. This also means the version on AMO is often incompatible with the latest version of firefox (as is the case now).