This looks like a change made by Google. If you right-click that input field and open the Inspector then you will notice that this is a textarea with one row (rows="1"). However, when I press the Enter key then I submit the form, Shift+Enter gives a linefeed. If that isn't working for you then you may be blocking JavaScript.

If you use extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) that can block content (Adblock Plus, NoScript, DuckDuckGo PE, Disconnect, Ghostery, Privacy Badger, uBlock Origin) always make sure such extensions do not block content.

• make sure your extensions and filters are updated to the latest version
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

@cor-el

Thanks for your advice.

Using the Refresh Firefox feature fixed the problem.

(It also removed all Firefox extensions.)

This question has been locked because the original author has deleted their account. While you can no longer post new replies, the existing content remains available for reference.