mp4's won't play in browser

I have been rendering from After Effects without a lot of messing around in Media Encoder settings, and until recently I get .mp4 animations that play in browsers, etc.

Recently AME has been producing mp4s that no browser will open; the available offered apps are QuickTime Player and Books and something called Handbrake. (Also, in QuckTime Player the color is extremely washed out; I think I have all Photoshop source files and PS and AE working spaces set to sRGB).

I may have done something when I was trying to adjust AE's color space; I don't know. But now even when I choose something designed for web, like a Facebook preset in AME, the rendered file will only open in QuickTime.