but how does edge get opened? firefox, and pretty sure chrome too, aren't searching the OS file associations for each asset they received from the site. they won't decode the png images with Windows Photos or whatever, they will use their internal tools to process it.

file associations would only affect if you open an svg file in the filesystem with a file manager. but I don't see how edge gets into the picture when the user is just using another browser, because it's rare that a user saves an SVG