In latest Firefox version 40.0.3, you can’t install Featured Add-ons from the Add-ons Manager, when you attempt to do that, you’ll get this error or warning: ‘services.addons.mozilla.org Firefox Prevented this site from asking you to install software on your computer’.
Mozilla is aware of this bug and has been marked as ‘Resolved Fixed’, but the target milestone was set to ‘mozilla43’.
To reproduce this on Firefox release
1. Visit Add-ons Manager > Get Add-ons> Featured add-ons
2. Select any featured add-on and click ‘Add to Firefox’
How many of you actually install featured add-ons shown by Add-ons Manager?