List of steps to reproduce:

• Visit a page with a score on desktop, e.g. https://en.m.wikipedia.org/wiki/Help:Score
• Visit the same page on mobile, e.g. https://en.m.wikipedia.org/wiki/Help:Score
• Tap or click on the score image in each

What happens?:
On desktop, a pop-up appears with a link "Download MIDI file". On mobile, there's no such link. I think the ext.score.popup JavaScript simply isn't loaded because in extension.json the resource module isn't targeted to mobile.

What should have happened instead?:
Offer the same download MIDI functionality on mobile. This is a minor glitch, but I'm not sure it was intentional when @Albert221 added the functionality in T183736; maybe T127268 is relevant.