A surprising revelation...On this[0] page, it says the add-on is derived from bitcoin-prices, another Firefox add-on. On the Github page of bitcoin-prices,[1] the license is GPL v3. The license file was added on July 14, 2013, but the last update of bitcoin-ticker was on March 29, 2013.
[0] https://addons.mozilla.org/en-US/firefox/addon/bitcoin-ticker/ [1] https://github.com/frewsxcv/Bitcoin-Prices
