Impossible to play!

Problem 0 (the most important):
Promotion doesn't work. The game just hangs at the point when my pawn is on the last rank.
Problem 1:
The panel on the right does not appear. No way to resign or see how much time is left
Problem 2:
The buttons 'hi', etc are below the lowest part of the screen until the first move is made in a game.

You could try to change your browser to better one,for example Chrome or Firefox newest versions that are supported by Lichess.

From the lichess 2 blog:
Firefox 55+ gets full support
Chromium/Chrome 60+ gets full support
Opera 55+ gets reasonable support
Edge 17+ gets reasonable support
Safari 10.1+ gets reasonable support
Internet Explorer is no longer supported
Exotic browsers like Brave are supported if they have a modern rendering engine

From the seamonkey page:
SeaMonkey 2.49.4 uses the same backend as Firefox and contains the relevant Firefox 52.9.0 ESR security fixes

What happens if you use a supported browser on your device?

Ok, i think i will just stop playing for a while or play on the phone etc.

Sad though, it feels like 1990s where sites are designed for specific browsers.

If by that you mean "the latest version of all popular browsers, which is what ~98% of lichess users use then yes - exactly like that.

Awesome to see another SeaMonkey user! :-D

These days I'm mostly using Vivaldi, but I'll see if I can reproduce this problem in SeaMonkey (but please be patient as I have many projects ongoing and don't know anything about web development)...

@Doofenshmirtz To say that the site which is broken for some browser is not frequented by the users of that browser is to say ... nothing.
You know what... the sun doesn't shine quite as brightly as the moon, since the sun is only visible during the day, when it is bright already.

@Toadofsky Thank you. I am not in any sort of a hurry.

SeaMonkey was last updated July 2018. That's newer than almost all of the minimum browser versions in the supported list (Opera 55 came out one month later, Edge 17 a few months earlier; the rest are from 2017). It's based on a version of Firefox that's too old, though.

The latest unofficial nightly (or 2.57) build might work: