It's not a character set issue. It's just that none of your fonts have that glyph.
I'm on Linux, but after installing the symbola font (Arch package: `ttf-symbola`) and restarting firefox, the square turns into the proper thumbs up sign.
I'm on Linux, but after installing the symbola font (Arch package: `ttf-symbola`) and restarting firefox, the square turns into the proper thumbs up sign.
mkdir -p ~/.fonts && wget -O /tmp/symbola.zip 'http://users.teilar.gr/~g1951d/Symbola708.zip' && unzip -j -d ~/.fonts /tmp/symbola.zip Symbola.ttf