User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:43.0) Gecko/20100101 Firefox/43.0 Build ID: 20151223140742 Steps to reproduce: Upload a Video on Vimeo with h264 codec. The contrast of the video must have a blackpoint Level zero. simply fill it with pure black. Also add the strongest red color. all is standard SRGB color range Actual results: on vimeo the result is very flat on firefox. the blackpoint is not Zero anymore i guess it's Level 16 somthing like that. the deepest Reds goes more Magenta. All other browser like chrome or internet explorer works fine. i only test this on vimeo not on youtube etc.

on youtube is the same problem. the blacklevel is on 16 not 0. and the colors are not correct

Is it possible to attach such a video (or share a link), please.

If you have an Nvidia card, you can work around this by opening the Nvidia Control Panel, going to the "Adjust video color settings" page, select "With the NVIDIA settings", go to the Advanced tab and set the Dynamic range to "Full (0-255)". I'll mark this as a duplicate of bug 1161349 (which has been stalled for a while, unfortunately).

Yeah it's working, but It's not the solution for all the people who watch my Videos in the net. I cannot tell everyone that he must change the default settings ;-)