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You can download Firebug from http://getfirebug.com/firebuglite and integrate it as described on your homepage so it will load when the page loads.

But I see your point - I'll see what I can do.

The WebKit engine is not accessible at all - it's only possible to execute JavaScript to evaluate expressions in order to get the page title for example. 
Done - although I've never heard of that one until now :)
I've mentioned ideone is this topic: http://feedback.textasticapp.com/topic/7730-remote-source-code-compilation/
Wow - people are voting fast :)
Have a look at http://feedback.textasticapp.com/topic/102399-which-programming-or-markup-language-do-you-use-most-often-with-textastic/

If it works, I'll post it on Twitter.