This has bugged me for a while now, but normally I get around it by re-sizing the mIRC Script Editor to simply be really big, and forget about it after the irritation gets forgotten. Anyway, on to the topic at hand:
There are no "Maximise", "Minimise" and "Restore" options for the mIRC Script Editor (accessible by ALT+R from within mIRC). I don't see a point for not having these, given that the window dynamically resizes it's internal controls anyway when you resize it (using the "grab the corner and drag" method)
If possible please enable "Maximise", "Minimise" and "Restore" for the mIRC Script Editor.