Doesn't work in waterfox. The YT main page attempts to load an infinite number of videos to fill up the empty space, which is a problem I also ran into when trying to use ublock origin and blocktube to block videos on the main page - YT just replaces the blocked videos with new ones until all the empty spots are filled.
In the case of this add-on & YT's main page, both sides refuse to budge, so the browser gets stuck in a runaway loop of trying to load videos that will never appear, which freezes all tabs in your browser until you take matters into your own hands with task manager.
I'll update this review accordingly if this major issue is fixed in waterfox.

Useless with polymer off.