intent:
know when viewing non-FBA (not fulfilled by amazon) item pages
known requirements (Amazon design change of 8/5/2020 on Chrome only):
chrome: must be signed-out or have active prime account for the product page to include merchant info
firefox: still has old design and does not require active prime account or signed-out
what it does:
runs at or after page loaded (works with product variation menu buttons)
checks for "Fulfilled by Amazon" or "Ships from and sold by Amazon.com" or "Sold by\nAmazon" text in page item-info sidebar
checks for out of stock/unqualified/etc. item-info
if neither are found, then it puts a frame around the amazon body with blinking text label above it, and puts a blinking text label in the item-info sidebar