1) The vast amount of largely-useless add-ons it has;
2) Viewing pornography on the Internet;
3) Its obvious superiority to Internet Explorer (AKA IE);
4) Its obvious superiority to all other browsers; or
5) Its obvious superiority to life, the Universe; and everything else, including the kitchen sink and a unicorn's horn count.
Definition B. (noun): A synonymous term for red panda, which is an indigenous animal to Southeast Asia.
Definition C. (verb): A rapidly-spoken order from either an organization's boss or some other high-ranking officer, most often used to kick another employee out of their job. Usually, that said employee has either:
1) The given name "Fox;"
2) The surname "Fox;" or
3) The nickname "Fox."
Person 1: "Dammit, Internet Explorer just crashed on me again!"
Person 2: "Well, why don't you just use Firefox, then? It'll save you a lot of trouble."
Person 1: "Um, what did you say?"
Person 2: <inefficiently tries to explain what a Web browser is, and what Firefox is, and what its benefits over IE are, and so on, until Person 1 is finally convinced.>
(Later that week...)
Person 1: <goes on long rant about how awesome Firefox is.>
Person 2: "I know, right?!" (Etcetera, etcetera.)
Example of Definition B:
Some random person: "Red pandas are cute. No exceptions."
Example of Definition C:
Some CEO's Wife: "FORTHELOVEOFGOD-FIREFOX!!!!!"
Some CEO: "Okay, fine, whatever- I'll do it!"
B "Yo mom, in bed!"
A "Man, I am gonna smack the penguin into you!"
B "Yo mom smacked my penguin"
A "That goes for all you firefox haters, grow some balls!"
*Clicks on ad*
FORMER Internet Explorer User: Firefox...my master...
Dude 2: Yeah! But not Tracey though, she's a Firefox!