A few months ago I started having this problem with a newer version (4.2) I downloaded a few years ago and run from command line. The older version originally came when I installed Ubuntu still works fine. (I run the older version from the GUI.) I removed all the files in the firefox directory and downloaded the latest version (4.7). Same problem. I have removed the profile and pref.js files from .mozilla, that had no effect. I tried selecting the different options in Preference->Content->Color, that only affects the colors of the texts and background of the webpage, the texts I filled in remains white and invisible against the white background. The only way I could see them is to highlight them, then the background becomes orange, and I can see the white texts. I also have this problem when I type in a URL in the address bar, as well as the search box in Yahoo Mail. However I don't have this problem with the Google Search bar, nor do I have problem with most of the websites where I need to fill in texts. For example, when I type in texts in the search bar in this Mozilla support page, the texts are visible.