Putting in place an infrastructure to test this kind on changes on the 5-10 most popular browser would be, I think, very cheap for a company like Google. I can't help thinking these may be deliberate moves to eat the little market shares of Chrome concurrents. I remember reading here on HN an article written by an ex-Mozilla insider relating the dissonance between the "friendly" Mozilla-Google employees exchanges and the year-long track record of very oddly recurrent "unfortunate mistakes" from Google degrading the Firefox compatibility.