I just exported my iCloud password into a csv file on a MacBook, then imported that file into Firefox.

Agreed - I’m ready to bail on safari but don’t want to use chromium

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The Keychain integration is done through a Chrome/Edge browser extension developed by Apple. Hopefully they will also port it to Firefox.

Apple has made an iCloud Bookmarks extension for Firefox which is still supported, so hopefully a Keychain extension will follow.