Not compatible w Firefox for iOS
Fiatjaf's nos2x https://github.com/fiatjaf/nos2x
works on chrome and some forks (ie brave, afaik)
and the firefox version is called nos2x-fox https://diegogurpegui.com/nos2x-fox/
Discussion
hmmm there's a remote signer called amber, at android and f-droid... not sure if there could be one at apple's...