search your harddrive with keywords 'firefox' & 'mozilla' delete everything you find,
search your registry with keywords 'firefox' & 'mozilla' delete everything you find,
download the latest firefox version from a different site than you downloaded it from before,
install firefox.
search your registry with keywords 'firefox' & 'mozilla' delete everything you find,
download the latest firefox version from a different site than you downloaded it from before,
install firefox.