https://share.firefox.dev/2HXXj1C

Lots of time setting up the clips.

This perf is indeed terrible, but currently it doesn't seem to be cs_clip_rectangle. I see:

• 26% brush_solid_ALPHA_PASS_frag (draw_alpha_batch_container)
• 15% brush_image_TEXTURE_2D_frag (draw_alpha_batch_container)
• 12% brush_image_ALPHA_PASS_TEXTURE_2D_frag (draw_alpha_batch_container)

Still something to do with clip masks, though?

Oops. On a newer build, I'm seeing:

• 37% cs_clip_rectangle_frag
• 15% brush_image_TEXTURE_2D_frag (draw_alpha_batch_container)
• 10% brush_image_ALPHA_PASS_ANTIALIASING_REPETITION_TEXTURE_2D

Still bad post bug 1676554.

The clip rectangle overhead has mostly been resolved by bug 1682194. The rest of the overheads are still mostly living in fast paths that we can't do much more about for now. I am going to close this out to make room for newer bugs that might be more representative of problems.