Phew.
As it happens, you got lucky this time, because we do need that duplicate layer. You need to apply some Gaussian Blur to it - just enough to get rid of the distinct fabric lines, eg around your hand. I think about 0.6 will do.
Then mask that layer too.
Gosh, that's odd. No, no problems with Firefox and Windows 10 here.
Does it crash immediately when you launch Firefox, or randomly while you're browsing later?
No, it's to dangerous to put it on Duplicate, sorry. Leave it on Extend, and try making it the main display as I suggesed.
Sure, maybe that would help!
Don't worry about this. As I said, the computer will know.
Sorry, I've tried all the file formats I can think of. Nothing is working.
Brian might have some wiser ideas, but honestly, with the file sizes so small, I fear these files are unusable.