No Youtube with SM 2.53.4

Just installed the above on a W7 machine, can connect to Youtube, placeholders for the recommeded videos appear, but that's about it. 

There is nothing clicable on the page. Not even the filter button will work.

What the heck is going on!? And this is not the beta version, it's the standard relaese.

Maybe they don't support W7 anymore?

YouTube is working just fine for me using Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Firefox/60.0 SeaMonkey/2.53.4 with no extensions installed.

Have you tried safe mode using Help > Restart with Add-ons Disabled?

Well, this is bizarre. Downloaded and installed (in separate folders, of course)2.49.5 and onwards to see if there was some point in the version sequence where this problem first surface. 2.49.5 was fine, 2.53.4 not. 

Installed 2.53.1, that worked but then, suddenly did 2.53.4 - no more problem with Youtube. This was not some temporary glick at the Youtube end, either, because anothe machine running 2.49.5 was fine with Youtube.

Again, what the heck is going on?

I doubt that that will happen for a very long time yet. And see my subsequent post.

I'm also on Win7 still, but I have not encountered any issue with playing Youtube videos. All fine, beside of too high memory consumption.

Did you try it with a new Seamonkey profile? Maybe a former add-on has confused settings. Also, check whether an ad-blocker is enabled and maybe blocking a certain script for Youtube.

I set up a user-agent override in about:config, claiming to be Firefox 60. That works so far.general.useragent.override.youtube.com set as Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:60.0) Gecko/20100101 Firefox/60.0

No problems in my decade old, updated 64-bit W7 HPE SP1 PC. I assume your brand new SM installation has no extensions, non-default changes, etc.

Do you have a firewall or some security protections that could interfere?