edit passwords accross all browsers

Open each password manager installed, export all passwords, and migrate all into one password manager.

That’s probably not going to be a small project, and it’ll require details of each password manager.

Try again.

Here is how to migrate into Passwords app and the Apple iCloud Keychain password manager:

Import passwords from another password manager into Passwords on iPhone - Apple Support

By default, Firefox uses its own password storage.

Apple has available a Keychain extension for Firefox on macOS that allows Firefox to use the Apple Keychain mechanism for passwords. This extension was first made available at the end of 2024. I’m don’t know if there is an equivalent extension available for Firefox on iOS.

Whether you had (have) some third-party password manager also involved?

With no disrespect intended, reportedly given multiple different browsers, given multiple password managers, and given a mix of Windows and Apple gear, and given uncertainties with which passwords are stored where, and with few (no?) passwords stored in the Apple Passwords app and Apple Keychain, what would you have anyone suggest?

I’d pick fewer browsers and fewer password managers, but that may well not fit your needs and requirements.

Chrome and Firefox have long used their own password managers.

Apple uses Keychain and the Passwords app, and that storage is available for all Apple and third-party apps that choose to use it.

See Settings > Auto-Fill and Passwords.

Configure to use iOS’s Passwords app.