I'm not much of a profit, accepted, rejected, site watcher, but since you asked for favorite plugin, yes here's one I use and like.

EXIF Data Viewer (Mozilla Firefox)

Extracts and displays the Exif (Exchangeable Image File), IPTC-NAA/IIM (International Press Telecommunications Council / Newspaper Association of America / Information Interchange Model), and IPTC Core (Adobe XMP, Extensible Metadata Platform) metadata, as stored by digital still cameras, in both local and remote JPEG images.

https://addons.mozilla.org/en-US/firefox/addon/3905

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