The items in Firefox/Services menu disappeared after I restart my iMac, but not in every browser tabs. For example, they are there and working correctly if the browser display the Help/Troubleshooting page (I'm not sure the name is the correct one, I have a localized version in Italian: "Aiuto/Risoluzione dei problemi").

If I actuate Firefox's refresh function, Services work properly until I close and reopen Firefox.

I tried to run Firefox with the option "*-NSDebugServices com.apple.mail*" getting the following messages:

    Mail/New Email With Selection (com.apple.mail) is enabled in the services menu and disabled in the context menu, by the standard Services policy.
    Mail/New Email To Address (com.apple.mail) is enabled in the services menu and disabled in the context menu, by the standard Services policy.
    Mail/New Email To Address (com.apple.mail) is disqualified because its send and/or return types cannot be handled by the requestor ChildView 0x11b6e4680, gecko child 0x11ba56800, frame {{0, 0}, {1580, 1040}}.
    Mail/New Email With Selection (com.apple.mail) is disqualified because its send and/or return types cannot be handled by the requestor ChildView 0x11b6e4680, gecko child 0x11ba56800, frame {{0, 0}, {1580, 1040}}.
    GVA info: Successfully connected to the Intel plugin, offline Gen9 
    WebGL(0x12dc38000)::ForceLoseContext"
Please, do you have any idea how to fix my installation?

iMac Retina 5K Late 2015 -
OS X 10.11.6 -
Firefox 50.0.2

After the Firefox 50.1 release updated "*The song remains the same*"...
[![Services menu works in Firefox maintenace pages][1]][1]
but:[![it doesn't work in any other page][2]][2]


  [1]: https://i.sstatic.net/QWhMi.jpg
  [2]: https://i.sstatic.net/E9pdd.jpg