Extremely poor performance on Firefox Android

[kanashimia]

Landing page renders at like 10fps in Firefox on Android, which is pretty funny while reading performance claims.
Issue occurs in Firefox, but not in Chromium.

I verified two devices and two different Firefox versions, one of them is the latest nightly, one is an old stable.

I think this is because of the CSS, there are a lot of "fancy" stuff going on there, perhaps it is blurs or transitions or shadows slowing things down, but that is just a guess.

Specifically those pages are very slow:

• https://astro.build/
• https://astro.build/about
• https://astro.build/themes
• https://astro.build/showcase
• https://astro.build/blog/astro-021-preview

Those are okayish, but still laggy:

• https://astro.build/blog

Those are ok:

• https://docs.astro.build/

Landing page on a desktop Firefox too feels sluggish while scrolling, although it is pretty subtle and isn't as obvious.

[delucis]

I can also confirm this. We previously narrowed this down to some mix-blend-mode issues I believe and experimented with some alternative approaches here: #602

Not sure we were ever able to find a good solution.

[dandv]

Very poor scroll performance still present on Firefox 121 desktop on Linux. See screencast linked from #997.

[aaarichter]

@delucis this issue should be reopened - mobile firefox scroll performance is still very bad

to be honest - this is a red flag to me when deciding between astro and alternatives.