Oh no! What language is this?

I downloaded Firefox 3.0 Beta, but all of the menus are in a language that I do not understand! If someone could identify the language or at least tell me how to make everything in English again I would be overjoyed.

Here’s an example (from the top menu): Plick, Edycja, Widok, Historia, Zak(weird “l” like symbol)adaki, Narz(e with squiggle on bottom)dzia, Pomoc

Any help would be greatly appreciated!