Loading issues on stackoverflow.com/px.js [duplicate]

Since a day or two Stack Overflow never stops loading on my system. It displays the page correctly and as fast as usual, it just keeps the reload symbol spinning. The console throws the following messages about px.js:

When logging in, Firefox calls the Storage Access API on behalf of the site. See https://bugzilla.mozilla.org/show_bug.cgi?id=1949491 for details. stackoverflow-login.js:7:9
Loading failed for the 

The script it points to is:

window.addEventListener("OneTrustGroupsUpdated", setupBraze);

        
        
        

What is this px.js and why doesn't it load for me?

The same happens here on meta.SO with the following warning:

Cookie “__cf_bm” will soon be rejected because it is foreign and does not have the “Partitioned“ attribute.

Clicking on the linked attributes gives PNG images on i.static, i.e. user avatars.

System: Windows 11, Firefox 153.0.4 (Add-ons uBlock Origin, Privacy Badger, Tampermonkey with only 4 SOCVR scripts enabled)