As of today the situation changed a bit. It's now possible to download Minecraft for Linux on Firefox but it's not the default option. See below for comparison.
Linux, Firefox:
[media]
Linux, Chrome:
[media]
The page on Google Chrome looks okay, whereas on Firefox it looks like it assumes it's Windows.
i wont use any resouce packs, i just started at new world.
I confirm — everything works perfectly now. Chromium and Firefox on Linux show the same version. Thank you!