Compability: Paste Screenshots via 'ctrl+v' in test execution with FireFox

With IE it's always possible to paste a screenshot in test execution screen.

With FF it's only sometimes possible to paste a screenshot in test execution screen.

Steps to reproduce:

• Create a Test ticket
• Create a Test Execution ticket (out of the Test ticket)
• Go into the Test Execution ticket and click on execute
• Paste any screenshot via 'ctrl-v'
  • IE: Popup for saving screenshot every time
  • FF: Only sometimes (or some special conditions ) the popup is shown, in most cases no reaction

Popup: