reduce system usage of firefox by Add-On ToManyTabs

Today I have read in the Book DTrace about an investigation about the
CPU usage of the firefox  browser.
There was the hint about the Plugin ToManyTabs, which allows to move
open tabs to different rows, which act like closed tabs and the
CPU usage drops.

There is a small row in the header where you can switch between different
groups.
When you select an item it is moved to the open tabs and removed from the
group, but you can drag&drop it back to the row.