If you have chosen to login to Toggle with your Google ID, then this add-on will not work for you.
Create an account using email/password instead.

Tried to disable all my Add-ons and Privacy tracking, but got successful login.

Every day during the day plugin stops current activity and starts new empty one. Sometimes it starts brand new empty activity tracking even when I'm away from PC - so there are empty log of several hours during some work days.
It is caused only by the plugin. Toggle for desktop works fine so the iphone version works fine.

I can't open the settings page and it throws an error. It also could be better if it had more options (like deleting jobs or Pomodoro timer)

P.S. the lack of Pomodoro timer is probably because I can't open the settings page.

I've been waiting for the official Toggl add-on on Firefox since I moved from Chrome. It works great with Trello, and TargetProcess, which are the apps I use to track my time. Thanks for helping out Firefox users!