I'm the person who reported that. As a temporary workaround I'm using the Favicon Switcher extension (with a smaller file). You have to do it per Firefox instance; the settings aren't synced.
I've found the playlist -- it's called Alone Together. I've just started on the first episode and it's pretty cool. It's a fanfiction radio play!
The lemmy.world favicon is not being displayed in Firefox (but works in Chrome/ium). I'm pretty sure that this is because the currently used image is too large (it's 4267x4267 pixels and 365K, far larger than is needed for a favicon). Another instance encountered the same issue, and their favicon works now (after being reduced in size).
My very first WM was Blackbox, back in 2000, and I imprinted on it like a baby duck, so today I still mostly use Fluxbox. It's abandoned and unmaintained, but still works (for now). It's very minimalist and lightweight. When it finally dies completely I guess I'll finally learn how to use a tiling WM.
(I use Gnome on a laptop with a HiDPI screen, because that was too annoying to configure correctly on Fluxbox. It's... fine. I added a bunch of customisations and it mostly stays out of my way, which is what I want in an environment.)
No matter what WM/DE I use, I always add a dropdown / "quakelike" terminal application -- I previously used Yakuake, but switched to Guake. It uses a hotkey to show / hide a terminal (and you can use multiple tabs, and multiplexers inside the tabs). I can't live without this, and I highly recommend it if you often find yourself hunting around for your terminal window.
This happens to me all the time. It's a known issue which has been reported multiple times; #1375 appears to be the primary issue for this in the UI repo.