The Refresh feature (called "Reset" in older Firefox versions) often fixes this issue by restoring Firefox to its factory default state while saving your bookmarks, history, passwords, cookies, and other essential information.

Note: When you use this feature, you will lose any extensions, toolbar customizations, and some preferences. See the Refresh Firefox - reset add-ons and settings article for more information.

To Refresh Firefox:

1. Open the Troubleshooting Information page using one of these methods:
   • Click the menu button , click help and select Troubleshooting Information. A new tab containing your troubleshooting information should open.
   • If you're unable to access the Help menu, type about:support in your address bar to bring up the Troubleshooting Information page.
2. At the top right corner of the page, you should see a button that says "Refresh Firefox" ("Reset Firefox" in older Firefox versions). Click on it.
3. Firefox will close. After the refresh process is completed, Firefox will show a window with the information that is imported.
4. Click Finish and Firefox will reopen.

Did this fix the problem? Please report back to us!

Thank you.

Resetting will remove all data from the profile. However removing the account temporarily will remove this error and will request a fresh login token. Please try this first.

1. Open Firefox menu and click on the name of the sync account
2. A preference will open up, click on "disconnect account"
3. go to accounts.firefox.com and login with the same credentials.

If you have refreshed the profile and want to restore old user data please see these instructions: Back up and restore information in Firefox profiles

none of your solutions worked.

I seem to have solved this issue as follows:

• in preferences->sync uncheck Bookmarks
• Tools->Sync Now
• in preferences->sync check again Bookmarks
• Tools->Sync Now

no more error message :)