Rated 4 out of 5 stars
After a fresh install of firefox 4 RC, This installed without issue, though you do have to restart firefox in order to get the tabview button to work as advertised.
Fails to install (ff 4.0 b12) Rated 1 out of 5 stars
Cant get this to install (ff 4.0 b12) Stays on....
"A few seconds remaining - 15.6 of 15.6 kB (..."
Tried to manually install it too, but nothing seems to happen at all there.