Can you provide a screenshot?

Terry, I have been a bit slow to respond, as i have been waiting for my firefox to display the same message. A friend of mine suggested I change my mouse which I have, and I don't seem to be experiencing the same problem - as yet? That is until just started typing this message - the screenshot doesn't cover the tabs across the firefox ribbon which is where the message is occurring?

I suggest using your OS screenshot tool rather than the Firefox screenshot tool. The usual shortcut is the prt sc key.

Thank you Terry. Since changing my mouse, I have only experienced the problem once. As soon (if?) as the message appears again, I will do as you suggest and take a screenshot with my OS. Thanks for your help.