Those are the remnants of foam strips (pretty much like weather stripping), used to cushion the backglass. You can get similar foam from Lowes/Home Depot and replace.

Remnants of the factory foam rubber strips. Normal.

As are the marks they left on the back glass.

Don't replace these with foam. Use cork or felt instead. Over time, the foam reacts with the backglass ink and discolors it. Foam breaks down over time. Felt is probably the best replacement.

You know, someone gave me a tip on replacing that with the fuzzy side of an adhesive Velcro strip. I have yet to try it but it sounds promising.

I wouldn't use electrical tape. It's too thin to do any good, and the adhesive can eventually leak out toward the edges of the tape and gum up your glass. I think a strip of felt and a dab of glue would be best for cushioning the backglass.

This would be a simple solution but my concern is that the loop side of velcro could be too thick and bind/strain/stress the glass.

This is what I use. I take thin 3/4" wide felt weather stripping, which is maybe 1/8" thick and split it to about 1/16" thick and apply it to the head relay board with double sided sticky cellophane tape. It works quite well. I've found the 1/8" thick felt is too thick and can also bind/strain/stress the glass like I'm concerned the loop side of velcro might and that is why I split it thinner. A better solution could be if they make 1/16" thick felt weather stripping or just use black craft felting material cut to size.