Opening any sort of alert() freezes/softlocks browser

Self-explanatory.
Opening an alert() or prompt() on any page (I used https://www.selenium.dev/selenium/web/alerts.html) freezes the browser and keeps the cursor in pointer mode

Reproduce the issue using alert() and prompt() on the linked Selenium alerts page, then trace the browser runtime path handling those dialogs. No file or test is named in the issue, so first locate the relevant alert-handling entry point. Done means alerts and prompts no longer freeze the browser, and the cursor leaves pointer mode afterward.

Written by the indexing model from the issue text.