I don't know the technical details behind this, but Firefox always felt slower in file upload front. It was very late to the directory upload feature that Chrome had (in mostly non-standard ways I don't doubt).

It doesn't bother me to a point that I can't use Firefox, but for those who regularly upload files, I can totally see Firefox being a subpar experience.

I've noticed something similar with download speed; I accidentally discovered a while back that using wget to download the same file would run far faster than firefox.

> It literally started to take all the computer RAM

That's probably not Firefox, but the way Proton encrypts data client-side. The browser has to do a lot of heavy crypto operations. At least that's the case with Filen.io[0]. I was told by support to have a beefy machine since the desktop web app encrypts data on-the-fly before uploading to their servers.

[0] https://filen.io/

If Chromium works fine it's clearly Firefox fault.

I used to wonder the same about Chrome. Try using a Chromebook with less than 4GiB RAM. You can handle 2 simultaneous tabs/apps---if you choose them well. It's due to this behavior alone that I never consider Chromebooks; by the time you find one with enough RAM to handle Chrome, you're in the price range of a "real" laptop.