This is more of a bug report than a question.

When I come back to Firefox after using another program and change tabs, sometimes the page displayed is from the prior tab that was selected. It is not selecting the new page appropriately. I have to click on another tab to change the page and then go back to the prior tab to then activate it. That always works, but my point is that the page should have been showing that corresponded to the tab I had selected. Seems to be a real bug. I have experienced that sequence many times now.