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Thanks, Fexxel. I was going to write more or less the same :)
That still doesn't solve the problem that you can't move the cursor up or down when the code completion list is shown, does it? 

Or do you mean that it would not be possible to choose a different entry than the first one in the list using the keyboard arrow keys? That could indeed be an option - not ideal but better than now for keyboard users. Just hit "tab" to accept the top-most entry and tap with your finger on the screen if you need select a different one.
Yes, MEL as in Maya Embedded Language is supported. Try to choose the correct syntax definition in the File Properties popover. It seems to use the same "as" file extension as ActionScript, so you'll have to select the syntax definition manually the first time.

If the correct character encoding is not detected automatically, you can choose a character encoding by tapping-and-holding the file and choosing "Open with Encoding".
Also, if I implemented it this way, I would probably not use the software navigation wheel for navigating the code completion. I think it makes little sense to use these arrow keys if you can just directly tap on the entry.

By the way: I'm really happy that you're taking the time to post your ideas here!
Must be an app store bug. For me it says "Updated: Mar 10, 2012".
But what if you want to move the cursor up or down instead and just want to ignore code completion? In other editors, you do this by pressing the Esc key to dismiss the code completion list. I thought it would annoy people if this wasn't possible. 
Make sure you have an internet connection before you try to enable firebug. The easiest way to reset Firebug and enable it again is by refreshing the web view. You can do this by either re-confirming the url using the address bar or by simply closing and re-opening the preview screen. Then just tap on "Enable Firebug" again using the action button.
If I find a way to have both I'll add it. It would probably be too technical and confusing to users who do not know the internals if I added it as an option.
That's an interesting alternative. The "save to camera roll" function is a good reason to do it that way - although I'd have to find a shorter button title...