Sounds that Firefox is using a font that can't display the ≡ (≡)

You can use this extension to see which fonts are used for selected text.

• fontinfo: https://addons.mozilla.org/firefox/addon/fontinfo/

The CSS was set with Helvetica or sans serif. I rendered it with no CSS and the default font still won't display it.

Do you have that problem with other symbols?

• http://en.wikibooks.org/wiki/Unicode/Character_reference/2000-2FFF
• http://en.wikipedia.org/wiki/Unicode_symbols

Okay, so this is what I did: I took the whole source code of that page http://en.wikibooks.org/wiki/Unicode/Character_reference/2000-2FFF which displays all the symbols correctly, but as soon as I changed the symbol tag from td to span it vanished. So it looks that when wrapped on some tags, the symbols won't display.

A little more information, I'm working on a Wordpress theme, but I did a plain HTML page with the same results. The symbol displays on Safari, Chrome and Opera, I'm yet to try it on IE.

Hey everyone, I found the solution. Turns out, I noticed the font family in my CSS was written as helvetica -all lowercase. I changed it to Helvetica, and voila. The character shows fine in Firefox. Seems like Firefox is more unforgiving than other browsers how you define your fonts on CSS. Still, that doesn't explain how the character doesn't show on pages with certain tags using the default font, but my particular problem is solved.