Some fonts have much more characters and symbols than you imagine. The problem is that most of them are hidden in Character Map and is hard to be printed by keyboard.

This addon displays mathematical symbols that are in most popular fonts. You can use them in most forums and pages, without any hesitation if MathML is supported.

IMPORTANT: you can open easyMath toolbar by pressing <control>+<m> or by selecting menu View > Sidebar > easyMath (not available in compact Firefox menu).