As reported in https://webcompat.com/issues/120699, Firefox has a fair bit of jank and may peg the GPU while loading and scroll on https://www.jetbrains.com/fleet/.

I've recorded a graphics profile on MacOS: https://share.firefox.dev/3omWODE
Another profile was recorded as well on Windows 10: https://share.firefox.dev/3zM452k

It's unclear to me whether the jank is caused by JS doing something to trigger repaints/image decodes, or if there are other clues in the profiles I'm missing.

Hmm, one thing I'm noticing is that the page uses webp images of size about 2000 x 1400, however their content is completely transparent except for a ~200x200 image. These images compress well, usually smaller than 16k. We use 16k at the boundary between "try to decode this sync" vs "decode it async". So we decode them sync, but pushing that many pixels takes more time than say if the 16k compressed image size wasn't devoted to 98% transparent pixels, ie usually 16k images are much fewer pixels. Perhaps we should put a pixel limit on sync decoding in addition to compressed image size.

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:tnikkel, could you have a look please?

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