If you have Firefox and AVG Antivirus installed on the same PC, you may find that at some stage you are unable to press the enter key in the location bar in Firefox, and have to resort to hitting the -> arrow to the right of the location bar manually.
This is caused by the “AVG Safe Search” addon for Firefox.
You will want to load up the Firefox Add-ons manager (Ctrl+Shift+a), and disable the “AVG Safe Search” add-on. This will require a restart of Firefox to take into effect.
Example of the addons screen, with the AVG Safe Search addon disabled: