Twitter, like many video playback websites, now uses HTML5 instead of Adobe Flash Player. Please navigate to the YouTube HTML5 page and let us know if there are any formats that your browser does not support.

The last time I looked into this, I had to give up after Twitter's latest round of changes. You can see that thread here: Video viewing issues with Firefox.

Hi there I went to the you tube page suggested and the following formats were marked ! H.264, WebM VP8, MSE & H.264 hope you are able to help Wesley.

Hi Gainzim, on Windows XP it's normal to have this pattern:

blue (HTMLVideoElement) - red (H.264) - blue (WebM VP8)

blue (Media Source Extensions) - red (MSE & H.264) - red (MSE & WebM VP9)

The reason "H.264" and "MSE & H.264" are usually red is that Firefox does not have a built-in H.264 (MP4) decoder and Microsoft never released the Media Foundation for Windows XP. I'm not aware of any way to solve that. The usual workaround is to find a way to show the content using a plugin (e.g., Flash or VLC).

VP9 is red because it is turned off by default, maybe because it's still not completely stable in testing. If you want to get the highest resolution on YouTube's built-in HTML5 player, you could try turning it on. This won't help with Twitter.

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful.

(2) In the search box above the list, type or paste webm and pause while the list is filtered

(3) Double-click the media.mediasource.webm.enabled preference to switch it from false to true -- which will result in this list of webm-related preferences (you might not have the last one):

media.encoder.webm.enabled => default => true media.mediasource.webm.audio.enabled => default => true media.mediasource.webm.enabled => user set => true media.webm.enabled => default => true media.webm.intel_decoder.enabled => default => false

When you reload the YouTube page, the last box should turn blue.