Sounds as if you removed something you need. Easy done. As bodad says, reinstall it.

Rather than digging around in the Firefox cache to remove cookies, better just to click on "Tools", open up "options", then select the privacy tab, and click on "remove individual cookies", which shows you all the cookies you have, and you can pick them off as you choose, or on "remove all cookies" which would get rid of them all, but shouldn't take away anything that Firefox needs.