Came across this gem today. I've lent my iPad to colleagues (I don't think I'll get it back), and needed to test a website for iPad compatibility.
Mashable has instructions for changing your Firefox user input string to that of the iPad:
Type “about:config” in the address bar, click the right mouse button, select New – String, and name it “general.useragent.override”. Then enter the value “Mozilla/5.0 (iPad; U; CPU OS 3_2 like Mac OS X; en-us) AppleWebKit/531.21.10 (KHTML, like Gecko) Version/4.0.4 Mobile/7B334b Safari/531.21.10″.