Overlay opening stutters on Firefox

[shockme]

When I click on the uMatrix button to open the overlay, instead of the overlay opening smoothly, it opens at a smaller size (the normal size) then switches to the bigger size (advanced mode) and then moves to the left and to the right for a few times before settling on its final position.

I'm attaching a gif, but it doesn't show the issue so clearly as it happens in reality.

When Firefox is sluggish (I have hundreds of tabs) the issue is very pronounced.

[shockme]

The gif makes it look almost smooth :) but it's very stuttery in reality. I don't think I can upload a movie on github, which would show the issue more clearly.

[gwarser]

uBlock-LLC/uBlock#996

[gorhill]

Pretty much everything has been done with regard to this.

You say "when Firefox is sluggish": well uBlock is using an HTML page to display its overlay, so if Firefox is sluggish, uBlock will be sluggish, it is expected.