There were a few security bugs in the first 1.0 version and since then Mozilla has come out with a number of updates. Currently, Firefox is at 1.0.4. Try downloading the new one, uninstalling the old and installing the new. You may have to reset some things but it should repair the issue. Normally, if you do a simply uninstall, then reinstall, your Bookmarks and homepage should remain the same. Many folks simply install over the top of the old, but since you're having issues with your current version, it might be helpful to uninstall first. Here's the link:

http://www.mozilla.org/products/firefox/

Hope this helps.

Grif