Unfortunately, it is almost a decade old well known FF bug (and now in Chrome too), which is not present in IE. All the Ctrl+T, Ctrl+Tab, Ctrl+W etc. keys just stop working when the focus is on a flash object.
The worse thing is, no one seems to know the fix for it yet (see the thread above). Some IBM people made a hack fix for Linux, but there is none for Windows. It is really really annoying.
[update Mar 2013: In google chrome Version “24.0.1312.52 m” and I assume higher versions, the Ctrl+Tab key does not loose focus to flash]