The computer thinks the CTRL key is being pressed.
first, try rebooting the computer, to make sure one of your keyboard tables hasn’t been altered accidentally.
If that doesn’t work, jiggle the CTRL key until it appears to be moving smoothly and freely. Turn the keyboard upside-down, and shake it. Then try jiggling again. There may be something, a crumb perhaps, jamming up the free movement of that key.
Usually one or the other will work. If the problem persists in Firefox, you may need a new keyboard, but that is relatively inexpensive.