Correction: This mouse-click sound is happening in multiple Mozilla-based applications, not just Fir

Correction: This mouse-click sound is happening in multiple Mozilla-based applications, not just Firefox and Thunderbird, but also in other web browsers that are forked from Firefox. It does not happen in Chromium or Brave browsers, and it is not happening in other applications.

I have tried changing ui.click_sound in about:config to false, which did not help.