receive message '@mozilla.org/extension/manager;1' when opening mozilla - seems to happen when a second window needs to be opened? Help - this only started happening after mozilla upgrade?

I have four tabs that are opened when launching Mozilla - it launches a secondary window for one of the tabs, and the secondary window will not open until clicking ok on the mozilla message '@mozilla.org/extension/manager;1'. This only began happening after we installed the latest mozilla/firefox update. We have used mozilla for at least six years - first time we have had this trouble