Possible Duplicate:
How can I detect the current tab's mime type in a Google Chrome extension?
Is it possible from the extension background page to know if the active tab is showing a page or an html-less image?
I'd prefer to not use content page scripts, would be great to have the mime-type value in the tab object properties, but I could not find it ...
I don't want to just parse the tab URL, server-side generated images do not end with images extensions.