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You can get iCab and have the settings default as Firefox. I have this so I can access one site for some classes I am taking.
 
FireFox announced they are working on some sort of iPad app. Just read that a day or two ago, I forget where...maybe even here on MR actually. Or perhaps AppleInsider. But you can poke around and I'm sure find the info.
 
The Firefox app is not a browser. It uses the built-in browser.
 
Try Atomic Web... it's not firefox but I like it better than Safari :)
 
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