Can't Paste into Firefox Wayland

If I copy text from a non-Firefox application, either by CTRL-C or right-mouse-click/copy, I can't paste the text into a Firefox window, neither into the URL bar nor into an input field within a webpage. When I press CTRL-V or right-mouse-click/paste in Firefox nothing happens.

If I copy text from a Firefox window and paste it into another Firefox window it works. The issue is only when copying from a non-Firefox app and then pasting into Firefox. I tested pasting into weston-terminal, weston-editor, and l3afpad and they all work OK, only Firefox doesn't work.

I tested using Sway rather than Weston. Pasting into Firefox works OK in Sway, so the problem appears to be with Weston.

I'm running Weston 8.0 and Firefox 74.0 on Arch Linux. I start Weston from the console, open a weston-terminal, and then launch Firefox with "MOZ_ENABLE_WAYLAND=1 firefox"