File open dialog from button in browsed page fails

Use Firefox 77.0.1 snap on Ubuntu 18.04
Visit https://commons.wikimedia.org/wiki/Special:UploadWizard

Click on “Select media files to share”

Expected
File open dialog to pop up

Actual response
Nil

Similarly Firefox 76.x.x snap fails as well, but Works with firefox 68.9.0 esr/stable (snap)

Mozilla bugs directed me to report here. Please see https://bugzilla.mozilla.org/show_bug.cgi?id=1647047