[doublec]

For me following these steps using Ubuntu I get the Flash player both times. Did you get a preroll ad both times you tried it? They use flash (except for the MSE player). If you didn't get a preroll you may have got the HTML 5 player.

[wreegab]

I got the pre-roll ad, yes, which was also served as HTML5. I tried clicking more videos from the front page, so far all HTML5.

[doublec]

Interesting! I wonder what the difference is.

[wreegab]

I just noticed that if I switch to "https://", Flash-based videos are now served. Back to "http://", same video served HTML5. So this is it, "https" is the culprit (for whatever reason)?

Edit: On Chromium, "https://" or "http://" I get served HTML5.

So, could it be that Firefox somehow doesn't provide the proper cookie value telling the site to use HTML5 when using "https://" (I did set HTML5 pref with "https://")?

Edit: A cookie named "GED_PLAYLIST_ACTIVITY", used for "[e]ncrypted connections only", is used on Firefox only. I don't see this cookie on Chromium on an encrypted connection. So, there might be a link with the presence of this cookie and the serving of Flash-based videos.

[Sintendo]

I can confirm this is the behavior I'm seeing on Firefox. However, it's important to note that YouTube seems to force https if you're logged in, meaning logged-in Firefox users ALWAYS get the Flash player. I've resolved this for now by installing the YouTube ALL HTML5 add-on ( https://addons.mozilla.org/en-US/firefox/addon/youtube-all-h... ).

[touristtam]

Chromium/Ubuntu. Forcing HTML5 player gets me mostly: "video not available".