You can get some information with this servie.

Usage:
curl ipaddr.pl          # Get your external IP address
curl ipaddr.pl/headers  # Get HTTP request headers

URLs:
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Firefox extension: https://addons.mozilla.org/en-US/firefox/addon/ipaddr_button/
Google Chrome extension: https://chrome.google.com/webstore/detail/ipaddrbutton/jafoboipjndhmeocjapnkclkegmajdmd

Contacts:
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Pavel Kim (pavel@ipaddr.pl) https://github.com/pavelkim/