Hi @KristijanZic thanks for the feedback!
We’ve missed the single quotes in the tutorial, the array needs to be passed to the browser pristine:
$ snap set chromium-mir-kiosk url='["http://www.canonical.com","https://www.ubuntu.com"]'
As for your suggestions, think you could propose changes to the bazaar repo? Note this snap is a proof of concept, not a production-grade solution.