Firefox doesn't natively support the playback of quite a few video types.
The most common issue that arises from this is upon loading a viewing room link, it seems to get stuck on "Still loading video assets"
The first thing to check is whether or not you have Adobe's Flash player/plugin installed. You can check here: http://www.adobe.com/software/flash/about/
If after installing the plugin and restarting Firefox, the message still exists, then the video assets aren't compatible with Remark.
If you are a client/guest, please notify your project owner that you've checked for Flash and that there seems to still be an issue. You can tell the owner to contact us directly for support and troubleshooting on the issue.
If you are the viewing room owner, please check the encoding article for browser compatibility of your video files.