MacBook - Left Click = Right Click?

I'm having some issues with my track pad on my MacBook and Firefox.
I'll be either playing a game or doing something on the firefox browser and then I will switch screens to do something else with my itunes or what not. When I return to the Firefox browser and try left clicking something it will act as if I right clicked, even if no other fingers or anything other then that one finger is touching the trackpad at the time.

Any and all help would be most amazing.