I also tested in a focal VM with the firefox snap from the candidate channel (version 103.0-1), and I can confirm that in conjunction with the xdg-desktop-portal backport in that PPA the "Show in Folder" functionality works as expected.
I also tested in a focal VM with the firefox snap from the candidate channel (version 103.0-1), and I can confirm that in conjunction with the xdg-desktop-portal backport in that PPA the "Show in Folder" functionality works as expected.