Are you possibly using Private Browsing mode ? *https://support.mozilla.org/en-US/kb/extensions-private-browsing You can check that you aren't running Firefox in permanent Private Browsing mode (Always use Private Browsing mode; Never Remember History) as that can restrict extensions. *https://support.mozilla.org/en-US/kb/private-browsing-use-firefox-without-history *https://support.mozilla.org/en-US/kb/common-myths-about-private-browsing *Options/Preferences -> Privacy & Security<br>Firefox will: "Use custom settings for history" *remove checkmark: [ ] "Always use Private Browsing mode"