a firefox website hijack my macbook refuse to shut down

If necessary, force Firefox to quit by holding ⌘ option esc, choose Firefox, then the Force Quit button. Acknowledge the dialog with the Force Quit button. Close the Force Quit Applications window with the red button.

Hold an option key while starting Firefox again. Select the relevant options, then Continue in Safe Mode or Make Changes and Restart.

Don't visit whatever page it was that held Firefox hostage.

If you are being told by that web page that some law enforcement agency has locked your computer, and that you need to pay to unlock it, that's a scam. It's also, despite what you may find online, not actually a virus. It's just a JavaScript hack that prevents your browser from closing, and no more.

As John says, you simply need to force Firefox to quit and then make sure it doesn't try to re-load that page when you open it again. There is no removal needed.

For additional information, see:

FBI ransomware “virus” rampant

(Note that the FBI version is just the one used against folks living in the US. If you live somewhere else, it'll be a different agency, but that doesn't mean the scam behaves any differently.)