Created attachment 8787144 [details] kantar_media_virtual_meter-2.0.3-fx.xpi User Agent: Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/52.0.2743.116 Safari/537.36 Steps to reproduce: With no Firefox process running on Windows, use the command line: firefox.exe -p default kantar_media_virtual_meter-2.0.3-fx.xpi Actual results: We have the error message: Firefox prevented this site from asking you to install software on your computer Expected results: Firefox shall ask to install the plug-in, not prevent to install it Our extension is fully reviewed and signed by the developer add-on portal This was working perfectly well until version 47.0.1 Strange thing is that, doing it in two steps is working with version 48.0.2. That is to say that if I run these 2 command lines (No Firefox processes shall be running): - First: firefox.exe -p default (in order to start a Firefox process) - Second: firefox.exe -p default kantar_media_virtual_meter-2.0.3-fx.xpi Firefox 48.0.2 ask to install the plugin correctly. It seems that if we want to install the extension using the command line, Firefox shall already be started.
Update: This is working now. Did you change something on the backend side (AMO site). Same Firefox 48.0.2 installer, same tests and now it is working !!!!
Based on your comment I will close this as resolved WFM. Please feel free to reopen this bug if you encounter any issues.