Hi AD.B, Firefox 43+ requires that extensions be digitally signed by Mozilla. This article has more information: [[Add-on signing in Firefox]]. I'm not sure whether or when Trend Micro will be updating to signed versions of its extensions. Are you sure you have the latest program (not pattern file) updates? If updating doesn't help, you could make a temporary global exception to the signing requirement. Unfortunately, there's currently no way to only make an exception for specific extensions and therefore you need to be vigilant about bad add-ons creeping in if you do this. (1) In a new tab, type or paste '''about:config''' in the address bar and press Enter/Return. Click the button promising to be careful. (2) In the search box above the list, type or paste '''xpin''' and pause while the list is filtered (3) Double-click the '''xpinstall.signatures.required''' preference to switch it from true to false -- note that this is for '''Firefox 43-45 only'''