ref: https://github.com/snapcrafters/irccloud-desktop/issues/1
Core automatically updated somewhen to fix the regression with xdg-open, but already running or previously run snaps did not get their namespace reset at that time (expected, because we don’t want to go killing apps on updates unnecessarily).
However, upon quitting irccloud-desktop and relaunching it, the namespace still wasn’t reset so it still couldn’t open links. I closed and manually reset the namespace, which fixed it upon the next launch:
sudo /usr/lib/snapd/snap-discard-ns irccloud-desktop