Font Issues in jsMath
JsMath works best if you have installed some special math fonts on your computer. These are called the "TeX fonts" after the mathematical typesetting program for which they were developed. Although jsMath will work without these fonts, the results will be faster and higher quality if you do take time to install these fonts. Without these fonts, jsMath will fall back on using images of the characters in the font, or unicode characters from fonts already on your computer, or a mixture of both (which fallback method is used can be controlled through the jsMath control panel).
Versions of the fonts are available from the jsMath fonts download page, along with instructions for which fonts you will need, and how to install them on your computer.
If you do not have the TeX fonts installed, you will see a font warning message the first time you visit a site that uses jsMath. This informs you that you can obtain the fonts, and lets you either open the jsMath control panel, or hide the warning message so you don't have to see it anymore. If you do not intend to download the fonts, you can disable the font warning message using the jsMath control panel. If you save your settings for more than just the browser session, then you will not see the warning message again (until the settings expire).
If you install the fonts and the message continues to appear, be sure that you have put the fonts in the right place (see the instructions on the download page). One way to check this is to see if you can select the jsMath TeX fonts in a word processor's fonts menu. If you can, then you have the fonts in the right place.
If you continue to receive the font warning message, check that your browser settings do not prevent the web page from changing the fonts. Most browsers provide a means of forcing the page to use the fonts that you have set as your default fonts rather than using the ones specified in the page. If you have enabled this feature, jsMath will not be able to change to the TeX fonts, and will issue its warning message. You need to allow the page to change fonts in order for jsMath to function properly.
By default, jsMath uses six of the TeX fonts, but some page authors may use additional fonts. In this case, you may receive a warning message about needing a jsMath extra font. These can be obtained from the jsMath extra font download page. Download and install one of the .TTF files (either light or dark depending on your preferences) and test it by viewing the font table linked to the download page. If the page author has set up jsMath correctly, you should be able to view the page even without installing the font, but the results will be better if you do.