Have internet, but no video streaming

[Silent Warrior]

I feel I'm bashing my head against the wall, here, and maybe this problem will even go away on its own, but... Help me troubleshoot?

My internet is working fine. I can access this site, I can access other sites, I can watch YouTube on a laptop running Win10 (browser: Chrome) - but using the latest Firefox on Mint (20.2) no video streaming works. I've tried a few sites, and it's the same everywhere... The video downloads/buffers, but I don't get playback. I recently updated the kernel, but I have booted to it once already - and YouTube worked normally at that time. It's something I could experiment with, though.

I'm logged in as the same user on the Win10 laptop, so I can't have been banned or otherwise restricted on YouTube (or the other streaming sites). That also means it should be impossible that my ISP has introduced a user or connection-specific block on streaming. I have a PS4 running right now that doesn't complain about connectivity problems, but I don't use it for streaming.
My Mint-PC uses wired internet (... through a god-awful plurality of routers*, eventually passing through a wireless router, but still), my PS4 goes through the same wired mess, but my laptop uses wireless.

I have tried turning the wired connection off and back on, no reboot - no change. I have "restarted" the main router by pulling the plug and putting it back in - failed to find power button. Also no change. I only noticed this about a half-hour ago, so I haven't had time to do very much just yet.

* ... DO NOT ask for pictures. Giger-esque nightmare fuel.

[sleeper12]

Does it work in a Firefox private window?

[DAMIEN1307]

The video downloads/buffers, but I don't get playback.

It sounds like a permissions problem from the browser itself such as "enable DRM for protected video playback" etc...I dont use Firefox myself, but thats where i would start looking...DAMIEN

[Silent Warrior]

... What even... And now it works again. Dumb PC! Maybe power-cycling the modem and then restarting the PC did the trick? Cosmic rays, excess static electricity in the room for whatever reason? Graphics card having an off day? Weird.

I did look at the browser configuration, and I thought the DRM-content thing might be a factor, but it was already set to enable.