input to notification goes to originating window

I've been troubled by two problems:

1. Clicking notifications didn't do anything
2. Tabs were disappearing from my browser window, seemingly at random

Today I noticed that that is because my mouse input goes to the window that spawned the notification. Clicking anywhere will just 'fall through' to the part of the window that is occluded by the notification frame (even on on an otherwise empty workspace).
For browser notifications, that means I can click on the burger menu, the 'extensions' button, open the 'downloads' pane, or fumble with my Firefox tabs.

1. Go to https://www.bennish.net/web-notifications.html
3. Open a notification
4. Try to click the cogwheel
5. The burger menu of firefox opens
6. Switch to a new workspace
7. Click the cogwheel
8. The same happens (the burger menu opens despite Firefox being on a different workspace)

I'm on EndeavourOS, there's an `exec mako` in my `config.d/autostart/applications` - no other customisation.