The message will go away once you look at the new add-on from the message or from Tools-> Add-ons it is probably an upgrade to an existing Add-on, and possibly you need to make a decision as to whether it should be enabled or not.

• see also customising firefox / customizing firefox with add-ons

Thank you for the response. It corrected the problem. The problem was an add-on was trying to get into my Firefox, but it was for a version of the roboform toolbar that was newer than my current version. I jusat uninstalled it and poof, the problem is gone. Thank you again, John

Glad to have helped.