hello darcyK, please try to reinstall firefox:

• download the full firefox setup file from getfirefox.com
• uninstall firefox on the machine (but don't chose to delete your custom files & settings in the uninstaller)
• manually delete all remaining files in the firefox program folder, which usually resides in C:\Program Files\Mozilla Firefox\
• reinstall firefox

You can also try to run Firefox once as Administrator or reboot the computer and login as Administrator to see if that helps.