I've never successfully watched a video on Twitch. I get a black rectangle with playback controls, and when I press play, nothing happens. Disabling AdBlock doesn't help.

You have flash allowed on all domains without click to play?

I don't have Flash installed at all. Does the site require Flash?

If so, then that's news to me; other video sites that require Flash usually a) show a "you need Flash" message in the place where the video whould show, and b) don't show playback controls, because they're part of the Flash component itself. Also, I never saw any mention of Flash in any of the site's help/troubleshooting/FAQ documents.

It requires Flash, but it uses apple HLS.

I think Safari (+iOS) works without Flash, but everyone else is relegated to the Flash player.

Controls arein HTML5, just the actual video handler appears to be flash.

In the past (probably 2? years ago) the entire player including controls was part of flash.

Good to know, thanks.

Since posting my last message, I looked at the documentation on the website again, and saw that it claimed that you could use the site on iOS and Android by just using an ordinary browser. So I tried visiting it in Safari on my iPhone, and the videos worked. Then I tried using Firefox on my Kindle Fire, and the videos didn't work. But they do have a dedicated Twitch app for the Kindle, so I downloaded that. So now I have a way of watching Twitch videos. :-)

The fact that Flash is not mentioned anywhere on the site as being a requirement seems like a glaring omission.

"ordinary browser" = Chrome for Android, latest version, Safari for Mac, Safari for iOS

Firefox does not support HLS in either desktop or mobile version. It requires Flash as a last-ditch fallback on any platform that doesn't support HLS, afaik.