open a new tab
type: about:config
Accept the prompt
type middlemouse.paste
change value “true” to “false” (double click or switch on the rightside)
restart firefox
--does this solve it?It's copy that's an exploit vector.
To disable it, set clipboard.autocopy to false.
EDIT: I thought the behavior was preserved for textareas, as the comment box here still copied on select. But it suddenly disabled it here too. Restarting the browser is probably a safe bet :)
Say you're about to copy a crypto wallet. You have it selected, and are about to press CTRL-C to copy it. It is entirely possible for malicious code to detect that. And, as it turns out, it's possible for it to change the selection to a different (invisible) string, right as you press CTRL-C.