Not sure if it qualifies as an easter egg, but visiting Mozilla developer website like this with your console open and you’ll get the following message:
_.-~-. 7'' Q..\ _7 (_ _7 _/ _q. / _7 . ___ /VVvv-'_ . 7/ / /~- \_\\ '-._ .-' / // ./ ( /-~-/||'=.__ '::. '-~'' { ___ / // ./{ V V-~-~| || __''_ ':::. ''~-~.___.-'' _/ // / {_ / { / VV/-~-~-|/ \ .'__'. '. ':: _ _ _ ''. / /~~~~||VVV/ / \ ) \ _ __ ___ ___ ___(_) | | __ _ .::' / (~-~-~\\.-' / \' \::::. | '_ ` _ \ / _ \_ / | | |/ _` | :::' /..\ /..\__/ ' '::: | | | | | | (_) / /| | | | (_| | ::' vVVv vVVv ': |_| |_| |_|\___/___|_|_|_|\__,_| '' Hi there, nice to meet you! Interested in having a direct impact on hundreds of millions of users? Join Mozilla, and become part of a global community that’s helping to build a brighter future for the Web. Visit https://careers.mozilla.org to learn about our current job openings. Visit https://www.mozilla.org/contribute for more ways to get involved and help support Mozilla.
Nice.