Hi, websites ''can'' intercept Ctrl+U and turn it into an underline key. This is done with scripting. If the script is not already built into the site, then you'll just get the usual Ctrl+U response (View Source). Some sites' scripts may have custom script code for older versions of Firefox (older than Firefox 65) that hasn't been updated for newer ones. For those sites, you might need to add an exception. This thread has an example of how to do that: https://support.mozilla.org/questions/1287827 Does that work for your problem site(s)?