howto break flash stealing firefox

[Paul S]

I prefer to use keyboard shortcuts to maneuver through firefox (and the 
rest of the desktop too).  For example, C-t will open a new tab.  C-w 
will close a tab.  A-b will give me the bookmark menu.

I notice when I watch certain content, i.e. flash or youtube movies, 
that the focus of firefox gets lock up and I can't break it out without 
a mouse click.

The manual says that "tab" or "F6" are supposed to move the focus, but 
they don't work in such a case.  Has anyone figured out a way to get 
firefox back without the mouse?

TIA