Wrong font in WebButtons & WebPopupMenus

I have recently noticed that the text in buttons and popupmenus is much larger when viewed in a browser on Linux. My site is hosted on a Linux server and everything looks fine in Windows and OS-X, but when I open one of the apps on a Linux machine, the text is too big to fit in the buttons and popups. This is true for both Chrome and Firefox running under Ubuntu and CrunchBang. I don’t know if this is a bug or I don’t have everything set up right.

Does the linux machine HAVe the font installed that you’re trying to use ?

The web app just uses the system font. There are a few places where I made it bold or changed the color, but otherwise, I have done nothing with the fonts. Take a look at http://www.ezmeter.com/cgi-bin/catalog/metercatalog.cgi. With Windows and OS-X browsers, all the fonts except the titles are the same size. With Linux, the fonts in the buttons and popupmenus are bold and several sizes larger. As best I can tell, the font family is the same.