Currently, Firefox Mobile only allows passwords to be synced from a Firefox Account — there’s no way to import passwords directly from another browser or from a .csv file.
It would be extremely useful if Firefox for Android and iOS included a built-in “Import Passwords” option, similar to the one on desktop. This feature would make it much easier for new users migrating from Chrome, Brave, Edge, or other browsers to start using Firefox Mobile without needing a desktop computer.