Support for the <blink> tag was dropped in Firefox 23 in August 2013[0][1]. In February 2013, Opera had announced that it would switch from its Presto rendering engine (which supported <blink>) to WebKit (which never did). Since Internet Explorer's Trident rendering engine never supported <blink> either, this would leave Firefox's Gecko as the only rendering engine to support it. In April 2013, Chrome forked WebKit to create its own rendering engine called Blink[3] (named, ironically, because it doesn't support the <blink> tag.)

[0] https://bugzilla.mozilla.org/show_bug.cgi?id=857820

[1] https://www.mozilla.org/en-US/firefox/23.0/releasenotes

[2] http://dev.opera.com/blog/300-million-users-and-move-to-webk...

[3] http://blog.chromium.org/2013/04/blink-rendering-engine-for-...

This was the HN discussion when <blink> support was dropped from Gecko:

http://news.ycombinator.com/item?id=6170392