If you haven't already, take a look at the recent update. * Release Notes: https://www.mozilla.org/en-US/firefox/120.0.1/releasenotes/ * https://www.mozilla.org/en-US/firefox/all/#product-desktop-release One possible issue is security software preventing Firefox from spinning up child processes, which are how tab contents are drawn. If you check the Windows Task Manager (Ctrl+Shift+Esc), does it look like Firefox is able to start at least 3 firefox.exe processes at startup?