We have added a series of site compatibility documents for Firefox 16, released 3 years ago today, for the record. Those documents were originally posted to a Japanese Mozilla community site.
Firefox developers tend to avoid making drastic changes to Firefox releases maintained for a year as Extended Support Releases, including Firefox 10, 17, 24, 31 and 38. They rather work hard prior to a stable ESR and that’s why Firefox 16 had various changes affecting backward compatibility.
Those changes are actually interesting — from a bunch of unprefixing, object removals, property additions, de-support of insecure SSL certificates to a UA string change — like a showcase of site compatibility topics! Based on those archives among other 350+ documents, we will cover how to make a future-proof site in the upcoming blog posts.