Works fine in Chrome. Windows 7 Home Premium. Firefox 70.0.
What error do you see?
This add on is working in 2 browsers (1 Firefox and 1 Chrome) but a 3rd browser (Firefox) is giving me the message "Sync Bookmarks is not active" and "Locked"?
Could you send screenshot with problem?
I also have this problem. I have just set up a new PC with Firefox Quantum 68.11.0esr (64-bit) and added Eversync extension. When I click the Eversync icon (top-right of the browser window, it shows 'Sync Bookmarks is not active, a 'Locked' button and 'Initializing 0/0'. I have also installed Google Chrome 86.0.4240.75 (Official Build) (64-bit) and the Eversync extension. On Chrome synchronisation works fine. On my old PC I had Firefox Quantum 68.7 (64-bit) and Eversync works fine.
Did you check on actual Firefox version?
I put the information from Help - About. Is there some other way to get the version number?
Did you try to download latest version from mozilla.org?
I downloaded and installed 81.0.2 (64-bit). The synchronisation works now. Thank-you.
Customer support service by UserEcho