Platform: (forked) UXP
Browser: (latest) Serpent 52.9.0 (2022-02-25) (32-bit)
Extension version: 1.2.14b2
Browser profile: Fresh (with default settings), with only this extension installed

STR:

1. Visit/load e.g. :

https://github.com/JustOff/github-wc-polyfill/commits/master

2. Move cursor to the "Copy the full SHA" button of top commit,

, click button

3. Expected behaviour: Full (40 chars) commit HASH copied to the clipboard (with a visual indication of a successful copy action)

4. Actual result: Clipboard is empty (or contains whatever string was put there, via whatever, immediately previous, copy action)...

5. In contrast, on a Chromium-based browser sanctioned by GitHub, this is the visual result of clicking the button in question:

and the clipboard becomes populated with 1291c0573ddaa116c48386110ffe5c6a4fe751a3 ...
Nothing I could spot stands out in Web/Error Console... 😞