Currently the extension does a very simple check before rendering the button: the page exists, it's in the NS_FILE namespace, and user->isNewbie() is false. On the English Wikipedia this button should not be visible for files categorized in "All non-free media" or "Wikipedia files not suitable for Commons". For other languages these categories will likely be different. For the Farsi Wikipedia, they actually disable it through Javascript for certain categories.
This would help with the possibility of a user clicking the button and being disappointed when FileImporter gives an error because the file doesn't qualify import in to Commons.
Alternatively, if there were a way to determine if FileImporter would decline the image and omit the button in that case altogether, that could work too.