Brand new install of 17.10, love it so far. I especially love the new Firefox browser but I can't seem to get my videos to play on photos.google.com. All I get is a static screen with "This video format is not supported".
I did install Chrome and they do play through that browser, so I know I'm just missing something on my Firefox install. I tested Flash and that seems to work on the Adobe flash test site after I allow it, but I never get a prompt to allow Flash on the Google photos page, I assume they're using something else anyway.