Emoji are hot (possibly even, ATSUI? ha ha!) on iOS and Apple introduced an emoji font, complete with little colour smilies, for 10.7. Firefox even supports this font, sort of (there are some bugs in this support and in fact I had to back this out partially because of the secret flawed CoreText in 10.4 which interferes with Mozilla's Cairo-based emoji rendering).
Naturally the good versions of OS X, which is everything before Lion, don't have direct emoji support, let alone those fun little colour icons. However, if you're willing to accept a monochrome non-animated substitute, you can get emoji on your Power Mac, because emoji are really just Unicode characters at their most basic and if you could find a font that had the emoji in the right place in the character map, it would "just work."
Fortunately, there is such a font, and that font is Symbola. It works just fine with OS X, and with TTConverter will probably even work for OS 9 and Classilla. Warning before you install: when you try to do so, Font Book will freak out (correctly), saying the font is missing OpenType information. While it appears to work fine without it on 10.4, installing this font is of course at your own risk. Just unzip the file you get, double click to open it in Font Book for installation, and after installing it (and saying "yes, I don't care if my computer blows up") quit and restart TenFourFox to ensure it recognizes the new font.
Now you can see my cat, instead of a "no character here" box: 😺
Issues 194 and 195 are now fixed, though I'm thinking of even faster ways to enumerate fonts, but this still should cut down on lag with people who have a lot of fonts even in this state. And, since we've just added another font, that should help that much more. Yatta!