I played around with my settings this afternoon and discovered the following re the above:
I turned compatibility mode OFF and I no longer have the black boxes for YouTube links, BUT even though I have Ad*blocker enabled, my page is now full of ads!!!
Worst of all, each of the problems I had previously have returned, i.e. I can't add pics, edit posts etc etc.
I had no choice but to re-enable Compatibility Mode again. So now I can't post YouTube links or clicking on anyone else's either!!!
Why we have these issues on this forum is just totally beyond my comprehension because they don't happen anywhere else.
Bye ... until next time.