1. Open FireFox and go to Tools >> Add-Ons and remove the Hide My IP extension.
2. Then restart FireFox and navigate to: http://www.hide-my-ip.com/hideip.xpi and follow the instructions to install the extension.
3. A dialog may pop up asking you what program to open the extension with, select "Other"
4. Then select "FireFox.exe" in your "Program Files\Mozilla Firefox" folder.
5. Then either reboot your computer
6. Then restart both FireFox and Hide My IP.

Note: Also be sure a proxy is set in FireFox by going to the Tools, Options, "Connection Settings" window. When Hide My IP is running, you must see an IP address in your LAN or Connection Settings.