Browser: Latest (UXP-based) Serpent 52.9.0 (2022-02-25) (32-bit)
Browser profile: Fresh/clean one (with default settings), only this extension installed
Extension version: Latest release, i.e. v1.12.15

STR

1. One of my bookmarks is

https://github.com/coletdjnz/yt-dlp-dev/commits/itv-fix

FTR, that URI did have content until very recently, when the repo's owner deleted the itv-fix branch...
If you visit that URI now, you'll get a familiar "Page not found"

404 - This is not the web page you are looking for.

result...

2. Try to access your GH account's avatar button, on the top-right, e.g. to sign out/change an account setting, etc.

expected result: The familiar dropdown should open:

(Chromium-derived browser)

actual result: The dropdown informs:

Sorry, something went wrong.

(St52+gh-wc-pf-1.12.15)

Errors are shown in Web Console:

TypeError: window.customElements is undefined[Learn More]  vendors-node_modules_github_clipboard-copy-element_dist_index_esm_js-node_modules_github_filt-19a0ad-b0aa79d964b0f0b0715d.js:1:14977
ReferenceError: customElements is not defined[Learn More]  element-registry-f2d13d7793cb74e9c058.js:1:231
TypeError: window.customElements is undefined[Learn More]  behaviors-df903b53ab15748a5077.js:1:4217
TypeError: window.customElements is undefined[Learn More]  vendors-node_modules_delegated-events_dist_index_js-node_modules_github_catalyst_lib_index_js-6e358f-064c9c0434d0fad1cfc8.js:1:8547

Thanks for your efforts 👍 , I feel somehow guilty, though, for hitting (and reporting) many bugs recently... 😜 😄