Rated 3 out of 5 stars
nice and fast and i like that changing tabs does not require 2 clicks, one to remove focus from preview and a second to activate the 'other' tab... But... there are previews of loaded pages only. FF stopped preloading background pages somewhere around FF nightly 13 or 16, so if you could keep the speed and single click lose focus / gain focus, this would be the Best.Good Job.Landis.
ps, i realize i can 'reload all tabs' to generate previews, but i have between 4 and 6 windows and some 200 to 300 tabs, so not a good option.