The shortcut to open a new tab is "Ctrl+T", so you may have a stuck Ctrl key if this happens when you only press the 't' key.

Try to press all the status keys (Shift, Ctrl, Alt) a few times to see if that helps to recover from this. If it doesn't help then close and restart Firefox or reboot the computer.

Start Firefox in Troubleshoot Mode to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration or if userChrome.css/userContent.css is causing the problem.

• switch to the Default System theme: "3-bar" menu button or Tools -> Add-ons -> Themes
• do NOT click the "Refresh Firefox" button on the Troubleshoot Mode start window

• https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

I have the same problem...it is not a stuck CTRL key (if it was, hitting shift/alt would launch the log out screen). I've rebooted the computer and restarted Firefox multiple times and, while it doesn't always happen, it does still happen (usually when I am responding to a post or inputting a response). Knowing this, I make sure that I am not pressing any other keys at the same time (of course, it hasn't happened yet when I was typing this). This is becoming a bigger and frustrating issue. I don't want to change browsers, especially since I have used FF seemingly forever, but unless I can get this addressed, I may have to. Thanks for any help you may be able to provide.

it is not a stuck CTRL key (if it was, hitting shift/alt would launch the log out screen).

Third-party software can emulate key presses for specific programs. Does pressing the W key close the current tab?

Does it still happen in Troubleshoot Mode?