It causes issues with other extensions (Tab Groups in my case) because it has not been updated to work with multi-process Firefox.

After adding the extension button to the toolbar I was able to click the button, log in, and start tracking.

My only wish is a, user definable, option to combine websites and apps as one. For example, I'd like messenger.com from the web and Facebook Messenger from Android to be counted as the same RescueTime Activity.

It works just fine. Remember to put the icon somewhere visible after installing by going to "customize" on Firefox. Signed in without issues.

Would be great if it worked. It didn't.

signup doesnt work

This addon is extremely useful to allow me to track my internet usage with RescueTime. I do not have any customisation issues with the addon and it seems to stay logged in. Hopefully more users will update/post their reviews. Make sure you get the latest Firefox version and keep your addons up-to-date to avoid issues.

The add on is quite good. I didn't encounter the customization issues and the add-on didn't change anything.

The setup was simple and it has become an essential productivity tool for me.