Created attachment 8560441 [details] Context menu User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:33.0) Gecko/20100101 Firefox/33.0 Build ID: 20141113143407 Steps to reproduce: Show a message including the compact headers right above it (where you can see the subject on the left and the senders email adress on the right). Right click on the email adress, select "copy email adress" (might be different wording in English, I use TB German). Actual results: Pretty much every second attempt to copy the address fails. I have been having this error for years and years over a lot of versions and on different computers. Expected results: The email address should appear in the users clip board.