Hi ragempa, Mozilla has announced a procedure for the publishers of extensions to submit them and get them signed by the Add-ons team. Probably IDM will do that eventually. But it shouldn't be mandatory yet... In the final release of Firefox 40 and 41, the signing requirement is not enforced, there is only a warning. If yours says that the extension is blocked because it is not signed, please check the following setting: (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 '''xpi''' and pause while the list is filtered (3) If the '''xpinstall.signatures.required''' preference is bolded and "user set" to true, double-click it to switch it to false ---- If that is already set to false, then there must be some other problem with the add-on that is causing it not to work. Could you check for updates to IDM?