EDIT: Thanks for the reply. I saw the link to some random reddit thread, but not that Github issue report. Refreshing with cache cleared (Ctrl+F5) with Iridium disabled/uninstalled immediately fixed the issue. Why reply to all of these users having this issue with these wordy responses when this is all you have to do?

Still, Iridium must have corrupted something in the site's cache, as no issue existed until I installed/enabled it for the first time in months (when I started using Enhancer instead). There's no way I'm going to blame the website for behavior that only occurs immediately after installing and uninstalling an extension, with no change in website coding, browser version, etc.

Updating review to 3 stars because of the feature evaporation (why not restore more functionality before releasing the code rewrite?). But for anyone else affected by this, try Ctrl+F5 for a full refresh while Iridium is uninstalled/disabled, and you should be good to go.

EDIT 2: Also, while trying to call me out for not using Reddit's search function (which is known to be garbage, by the way lol), you link to two threads, neither of which are referring to the issue I had. Guess you never looked at the screenshot I provided. If installing and uninstalling your addon immediately creates an issue that requires clearing the cache to fix, the addon is at fault. Obviously. Also, I didn't say this addon was malware, I said the behavior was on the same tier as that of malicious software (that is, 'things break if you remove it').

***

So yeah, was using Enhancer for YouTube for a long time with Iridium also installed, but disabled, since I liked Enhancer's feature set more, and figured running them both at the same time would cause conflicts.

Saw that Iridium had a bunch of updates recently, so I decided to try it out again. So I disabled Enhancer and enabled this. Saw many features were missing, so I swapped back. And the INSTANT I re-disabled Iridium, YouTube videos will NOT load at all, even if I restart Firefox in safe mode! Instead, the video area is completely empty, same color as the background, etc. Screenshot: https://i.imgur.com/al4WyRE.png ) The only way YouTube videos will load again is if I re-enable Iridium, and keep it re-enabled, even though it clashes with Enhancer when that's enabled too (e.g. videos will not autoplay with both extensions active, no matter what options I set). This all happened today, no Firefox updating occurred in between, nothing. YouTube broke as soon as Iridium was disabled. In fact, now, YouTube will never work while in safe mode, which obviously wasn't the case before. Uninstalling it completely gives the same result as disabling.

I see you reacting to other reviewers saying that there's no way disabling Iridium broke anything, that having it installed was taking care of some bug in the browser (and that reddit link does not at all describe the issue, which is that videos don't load AT ALL, it's not some FPS issue). But this is definitely the culprit. I don't know HOW uninstalling an extension managed to break the website it interacts with, but it did, 100%. Find out why, and fix it. Reporting the addon for abuse in the meantime, this is malware-tier behavior.