1) write a well crafted exfil payload to mozilla or chrome directory (there are sqlite databases and files that store eg. indexeddb content) 2) trigger a tab open to attacker's website, website takes the exfil data from indexeddb and posts it to the server (have something inocuous looking on that website - like a fake npm homepage or whatever, so you don't close it fast enough)

from one step process, this will become universally usable two step process