[kemayo]

There is not, unfortunately.

Apple has an extension for Chrome ("iCloud Passwords") that lets you use the keychain passwords there, but nothing for Firefox. It's less-restrictive than it used to be, since the extension used to only support Chrome on Windows, but they gave in back in July of this year and made it easier to use Chrome on Mac.

Apparently, Firefox removed a bunch of password-related APIs back in Firefox 57 that broke some existing keychain extensions[1], so it might not be Apple's fault that they've not provided a Firefox extension. There's no progress on Firefox bugs related to making such an extension possible again, that I could see.[2]

[1]: https://github.com/jfitzell/mozilla-keychain/issues/88

[2]: https://bugzilla.mozilla.org/show_bug.cgi?id=1650212