I don't see any add-ons/extensions that can disable built-in shortcuts. I've tried setting permissions.default.shortcuts to 2, then restarted FF and refreshed the page, but it doesn't help.

At https://support.mozilla.org/en-US/questions/1367908 there is a solution that worked for me for over a year. Then I had to upgrade to Firefox 135 today and it stopped working. I see no other postings about this. Am I the only person who's driven nuts by not being to assign keyboard shortcuts intelligently?

I was able to find a solution, however it may be a bit brute force for most people. To disable any keybinding or reassign it from the Firefox default, go into your about:config and enable userChrome.css editing. Then you access your internal files from about:profile and create a folder named Chrome with the css file inside. From there, add a command:

root{

   --keybinding-Shift-Enter: none !important;

}

This one disables open link in new tab shortcut, but you can reassign to anything. Goodluck!