(3rd edit)
If possible, maybe just do a add folder option! or toggle off the thumbnails.
This is my idea for if using a ton of wallpapers is causing lag.

I think adding a lot of wallpapers is a bit too difficult for this addon without an ssd, and really fast ram. Having to load from the temp over and over on shutdown, is just too hard on my pc.
I only noticed this after I shutdown my pc btw, closing the browser had no issues.
It might not replace my clearnewtab addon, but is still very good.
clearnewtab just doesn't have widgets.


*old*
Is their any way to make videos contain/stretch to screen?
Getting the gifs/images to stretch was easy with the css, but I can't figure out how to do it to videos.