Browser movie issues

I have irritations with Browsers, and movies. I have Slackware-15.0 & 3 browsers: firefox; Brave-1.56.9; palemoon-32.5.0

All 3 play youtube videos with sound. But on imdb.com, they vary on trailers.

• Firefox plays the trailers correctly.
• Brave plays video, but no sound.
• Palemoon plays sound, but no video.

The only hint I have for you is that brave & palemoon are configured for less tracking, more ad blocking, etc.

Palemoon also has issues with javascript, and will trip over the odd innocuous or known harmless website, hang for 30 seconds and then offer to stop the offending script. If I do, I get nothing from the page. If I don't, I'd still be waiting.