Rated 3 out of 5 stars

Works well in standard Firefox Quantum 58.0b3, but not track sites in Firefox Developer Edition 58.0b5. I tested addon on Kubuntu 17.10.

This review is for a previous version of the add-on (3.1). 

Are you using the add-on in standalone mode, or in conjunction with the RescueTime desktop app for Linux? If the latter, please make sure you have the latest version: https://www.rescuetime.com/get_rescuetime