I haven't used soundboard yet, but I'm pretty sure it isn't "just" an HTML5 file upload. Perhaps it's as you said, they run checks on the file being uploaded. Maybe it will work, maybe it will crash in some use cases because they don't have a polyfill for some specific API they use. So instead of dealing with user complaints about crashes they just disabled the feature.
I'm also not sure why you're upset with Discord for implementing DRM for uploaded files. If they don't, they will get sued by the companies enforcing that DRM, so hate on those companies instead.

There's really no reason to be mad at them in this particular instance. Their client is Chromium-based (Electron) so they will optimize their new features for that engine first. There's probably less than 5% users who Discord from browser, let alone Firefox, and I think I'm being generous with that number. Additionally, some things are harder to implement (or even impossible) in native web rather than Electron, that has all the NodeJS integrations.

Sadly, I was born with uncheck outable username disorder.

One of those is not like the rest and doesn't truly deserve to be on the list – "username checks out". All the others provide absolutely no value, while "username checks out", at least, lets you notice a potential humorous situation which you might not have noticed otherwise.

That's Trisha, isn't it?

Counter point:

Product (noun) - something that is made to be sold.

The software in question is not for sale, therefore is not a "product", and this post is not an ad.

I remember using QuickPic all the way back on Android Gingerbread. They sure had enough time to solve "All Problem".

The comics are by Dorkly, but the watermarks have been removed. Please credit the authors.