OK. I give up. [Hands-in-the-air emoji]
But some if those browsers are truly obsolete! Does the average mudcatter use an obsolete browser? Apart from IE.

And it's complicated. Different browsers may apply a different font to mudcat. Last time I checked mudcat didn't specify a font so the browser will use its default, which you may be able to specify. In Firefox I have mudcat in sans-serif whereas on most others it appears in serif. On Linux I specified Liberation Sans, on Android it will probably use Droid Sans. The default font in different browsers may lack some emoticons - you get a black/white square - sometimes with the unicode number in it - or have different glyphs for the same emoticon. On my Linux box some emoticons are in monochrome - which I prefer - others are in colour - perhaps they don't exist in my default font so the system finds it elsewhere.

And it will vary with the website encoding. Mudcat is using ISO-8859-1 so these emojis will &-encoded. A UTF-n site may get the emoji encoded differently.

So lots of reasons why emoticons are missing or differ.

Wife's iPad can't do line 2 - though it's a few years old.

BTW - if you get a blank square and wonder what the emoticon us, copy it and google it.