Try. > <img alt="x" src="eqn-221.png">⁠-Achse
> <mml:math><mml:mi>x</mml:mi></mml:math>⁠-Achse Unicode Character 2060 is called WORD JOINER and seems to do what you want. I have no idea if Mozilla supports it. http://unicode.org/unicode/reports/tr14/ may be helpful. Tim.
