The instructions to get the webpage to display correctly in Firefox are as follows:

Windows:
1. Open the fonts folder within the Firefox install directory.  In a standard installation, this is found at C:\Program Files\Mozilla Firefox\res\fonts
2. Open the file fontEncoding.properties within the fonts folder with a text editor such as Notepad.  It might be a good idea to make a backup copy of fontEncoding.properties first.
3. Find the line containing the symbols definition. It should look like:
     # Symbol font
     encoding.symbol.ttf = Adobe-Symbol-Encoding
4. Comment out the existing line by placing a '#' character at the beginning of the line.
5. Now enter
     encoding.symbol.ttf = windows-1252
The result should look like :
     # Symbol font
     # encoding.symbol.ttf = Adobe-Symbol-Encoding
     encoding.symbol.ttf = windows-1252
6. Save your changes to the file fontEncoding.properties and close Notepad.
7. Open the file C:\Program Files\Mozilla Firefox\res\mathml.css in Notepad and reverse the order of the items Symbol and Times in the line beginning with
     font-family: CMSY10, Symbol, Times ...
to read
     font-family: CMSY10, Times, Symbol ...
8.  Now save these changes, close Notepad, and restart Firefox.  The website should now display correctly.

 

For Linux:
The first step is to install the Windows Symbol font.  If you have access to a computer running Windows XP, copy the file "symbol.ttf" from C:\WINDOWS\fonts to your Linux machine. 
To install the font:
In the GNOME desktop environment, start nautilus, press CTRL+L to go to the location bar, and type "fonts:///".  Move the file "symbol.ttf" to this location. 
or
In the KDE desktop environment, open the KDE Control Center (kcontrol), and go to the Font Installer window under the System Administration tab.  Click on the add fonts button, and select the "symbol.ttf" file from where you saved it.
Once the font is installed, go to the Firefox install directory.  If you do not know where that is, bring up a terminal window and type "whereis firefox".  This command will show you several possible locations to look in, but a probable location to start is usr/lib/firefox.  Within the firefox install directory, go to ./res/fonts.  Now follow these instructions:
1. Open the file fontEncoding.properties within the fonts folder with a text editor such as gedit, kwrite, emacs, nano, or vi.  It might be a good idea to make a backup copy of fontEncoding.properties first.
2. Find the line containing the symbols definition. It should look like:
     # Symbol font
     encoding.symbol.ttf = Adobe-Symbol-Encoding
3. Comment out the existing line by placing a '#' character at the beginning of the line.
4. Now enter
     encoding.symbol.ttf = windows-1252
The result should look like :
     # Symbol font
     # encoding.symbol.ttf = Adobe-Symbol-Encoding
     encoding.symbol.ttf = windows-1252
5. Save your changes to the file fontEncoding.properties and close the text editor.
6. Open the file ./res/mathml.css in a text editor and reverse the order of the items Symbol and Times in the line beginning with
     font-family: CMSY10, Symbol, Times ...
to read
     font-family: CMSY10, Times, Symbol ...
7.  Now save these changes, close the text editor, and restart Firefox.  The website should now display correctly.