MARQUEE started out as a "feature" of very early versions of Internet Explorer, as a way for IE to differentiate itself from Netscape. (Don't hate Microsoft too much for this -- they were just following the lead of Netscape, who had their own proprietary tags. Heck, IMG started out as a Netscape-only tag.)
There was a real danger for a few years in the mid-'90s that competition between browsers would manifest itself in a proliferation of proprietary tags that only worked with one browser or another. The old "Best viewed with..." buttons that sites used to festoon themselves with (examples: http://cjihrig.com/blog/wp-content/uploads/2011/12/best_view...) were an artifact of this; they advertised that a site used one browser or another's particular set of proprietary tags, which was how you positioned yourself as "cutting edge" in, say, 1996.
Things are better now, thankfully. (Not much better, but better.)
True, but that's because whatever site can choose to rely on a cutting edge specced feature that the other browsers haven't implemented yet. At least it's not the 4 different companies trying to one-up each other.
But that’s what previous browser wars also were about: one browser implements experimental technology, all websites target it, etc.
Chrome has become the new IE in the meaning that it supports weird special stuff, but sometimes not the official W3C definition, and webapps rarely work on multiple browsers.
The IMG tag showed up before there was a Netscape.
You know that venture giant, the 'A' in A16Z? Long time ago he was marca without the initial 'p', maintained an emacs clone called Epoch, and also hacked away on a web browser called Mosaic:
