Yeah, and I failed to even find an option to open a local HTML file on mobile Firefox (for Android) just now.

That's a shame — things were definitely different in 2019 when I built the initial version; and mobile browsers were definitely a target I had in mind for the tool (especially when it comes to the recovery).

Instead of wrapping the existing tool into a mobile app, I'm thinking about standardizing the QR code format from the tool a bit more — so multiple, more task-specific recovering mobile apps would be possible. (Like, the one in your password manager detecting certain internal text formatting and importing the entries automatically and such).