[git-pull]

IE 5.5 with no box models would be a contender [1]

At Social Amp (2012), I was making cross domain single-page applications for sites like 1-800-Flowers, where we had to support back to IE6, but, since a tag was missing from the main website, we had to do some hacks to "shore up" IE6 so the padding would be there.

It's feasible to have some pretty sweet JS (backbone.js, easyxdm) on IE6. The limitation came from the engine's performance, stylesheet and js caps, and really strict rules on, dangling commas (memory is a bit fuzzy in which instances, but it'd crash our whole script). In some cases, there'd be no errors, and it'd just freeze it.

[1] https://en.wikipedia.org/wiki/Internet_Explorer_box_model_bu...

[bonzini]

Border-box is arguably more useful than content-box, so the IE5.5 is not a huge deal. You can make other browsers act like IE5.5.

Back in the day it was quite a PITA though.