I use MathML. Why? Because it just makes sense for mathematics on the websites.
On my DragonFly I had to do the following:
Installed X.org 6.8.1 or .2. Enable xfs (the X font server) by adding xfs_enable="YES" to rc.conf.
From ports install x11-fonts/ttmkfdir and x11-fonts/urwfonts-ttf.
(Note: download doesn't exist anymore.)
New and better instructions: https://developer.mozilla.org/en-US/docs/Mozilla/MathML_Project/Fonts
In /usr/X11R6/lib/X11/fonts/TTF do:
# ttmkfdir > fonts.scale
# mkfontdir
This will update fonts.scale and fonts.dir, check them with cat or more to see if they contain references to the extracted new .ttf files.
Change /usr/X11R6/lib/X11/fs/config to have /usr/X11R6/lib/X11/fonts/urwfonts-ttf added to catalogue.
Also add /usr/X11R6/lib/X11/fonts/urwfonts-ttf as a FontPath to /etc/X11/xorg.conf:
# xset fp+ /usr/X11R6/lib/X11/fonts/urwfonts-ttf
# xset fp rehash
Edited $HOME/.fonts.conf and added:
<?xml version="1.0"?>
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
<fontconfig>
<match target="pattern">
<test name="family">
<string>symbol</string>
</test>
<edit name="family" mode="append" binding="strong">
<string>Standard Symbols L</string>
</edit>
</match>
</fontconfig>
Added user_pref("font.mathfont-family", "Math1, Math2, Math4"); to $HOME/.mozilla/firefox/<profile.default>/user.js.
There seem to be some bugs still, at least in displaying the W3C test suite.