My Firefox 3.1 just doesn't know the nonstandard keyword "ltgreen" you are using. "lightgreen" works (yielding #90ee90 as it should), and so does #00FF00 (pure green), with or without quotes. Either your version has a genuine bug, or you goofed your tests.

Other browsers "understand" fancy "color" names such as "villagegreen".

Since I'm not a web designer, I'm not gonna tell you that <FONT> is deprecated...