I'm guessing from your post that you previously had spellbound running and then upgraded your firefox and then it stopped working or doesn't show up anymore. Please correct me if I am wrong there, but I'll continue as if this is the case.
With Firefox updates, especially between major releases, the javascript handling among other things may change drastically. Most of the configuration and add-on stuff for Firefox works through javascript config files. When you upgrade the format of one or more of those files may have changed drastically, so therefore Firefox may fail to even detect installed add-ons. Add ons themselves sometimes change to support newer versions of the browser.
If you go really long times between upgrades, the best method for upgrading is to back up your favorites, uninstall the existing Firefox, manually delete any leftover folders, both in the Program Files area and under your Windows user profile, then install the new version of Firefox, then install the latest version of all your plugins.