Can you describe what error message you're getting, in the Add-ons Manager or elsewhere? Or whatever else lead you to believe Firefox is blocking something. I don't see anything related to Avira on the blocklist. * https://addons.mozilla.org/en-US/firefox/blocked/ The only confirmed outstanding issue I can find is the following problem with page loading. Please do not post comments on bug reports unless you have technical details that would be relevant. See [https://bugzilla.mozilla.org/page.cgi?id=etiquette.html Bugzilla etiquette] for details. * [https://bugzilla.mozilla.org/show_bug.cgi?id=844714 Bug 844714] - Avira browser protection reportedly breaks incremental page loading