Extension may not work by default in permanent Private Browsing mode (Always use Private Browsing mode; Never Remember History). *https://support.mozilla.org/en-US/kb/extensions-private-browsing *https://support.mozilla.org/en-US/kb/extensions-button

Does it still happen in a [[Profile Manager - Create, remove or switch Firefox profiles|new profile]]? An easy way to test a new profile is to install [https://aurora.mozilla.org Developer Edition] and see if it happens there or [[Refresh Firefox - reset add-ons and settings|refresh your existing profile]]. Make sure you stay signed out of your sync account when testing.

You can try "Clear the startup cache..." via the "Help -> More Troubleshooting Information" (about:support) page. *https://support.mozilla.org/en-US/kb/use-troubleshooting-information-page-fix-firefox You can check for problems with the extension registry files in the profile folder. Try to reset the extensions registry and rename extensions.json (extensionsOLD.json) and rename/remove compatibility.ini in the Firefox profile folder with Firefox closed. *https://support.mozilla.org/en-US/kb/Profiles New files will be created when required. See "corrupt extension files": *https://support.mozilla.org/en-US/kb/unable-install-add-ons-extensions-or-themes You can check for possible updates in case of issues. *click the cog icon (left of the Search bar) on the about:addons page to "Check for updates" You can use the button on the "Help -> More Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the <b>about:profiles</b> page (Root directory). *Help -> More Troubleshooting Information -> Profile Folder/Directory:<br>Windows: Open Folder; Linux: Open Directory; Mac: Show in Finder *https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data