There are stating in their help page that Firefox allocates as much memory as the size of the downloaded files, which is not very convenient for this kind of application.

> However, some legacy or technically inadequate browsers require the entire file to be stored in memory for downloading (Firefox, IE10, Opera), or for both downloading and uploading (IE9, Safari 5).

At the end, the choice is yours but they are fairly warning you that the UX would be better on Chrome / ium.

Well I don't like their tone, I don't need to be told that my browser is "outdated", especially if it's not, it works perfectly fine for basically the rest of the internet, including web dev tasks. If there is a very specific use case for which it's not the best, they should have said so. They should have checked whether I'm using IE6, or the latest FF version, and adapt their speech accordingly. I feel like an angry nerd right now, but I'm the user this time so I'm right and they are wrong.

Why should Mega being going out of its way to make you feel better?

You can use Chromium.