Type about:preferences#content<enter> in the address bar. Across from fonts and colors, press the Advanced button. On the bottom, turn on Allow Web Sites To Choose Their Own.

This can be a problem with the font that is used to display the text.

You can right-click and select "Inspect Element" to open the Inspector (Firefox menu button or Tools > Web Developer) with this element selected.

You can check the font used for selected text in the Font tab in the right pane of the Inspector. Is that the Arial font or another font?

You can do a font test to see if you can identify corrupted font(s).

• http://browserspy.dk/fonts-flash.php?detail=1

You can try different default fonts and temporarily disable website fonts to test the selected default font.

• Tools > Options > Content : Fonts & Colors > Advanced
• [ ] "Allow pages to choose their own fonts, instead of my selections above"

i try this.. it's already marked..