The linked discussion thread is about plugins running in their own process in Firefox. Internet Explorer has had this feature since the launch of IE8, Google Chrome has had this feature since as far as I can remember, and even Safari, with its negligible market share, has this feature. I am using an unheralded browser on the Mac called Stainless - even that browser's team of maybe 10 developers has figured out a way to do not just plugins, but tabs in their own process. Whither Firefox?
I started using Phoenix 0.1 back in the day because I was sick of IE being stagnant, slow and bloated. Phoenix/Firebird/Firefox's claim to fame was it innovated faster vis-a-vis IE. Ironic isn't it - Firefox is the IE of today - slow, bloated and almost stagnant. Almost because it is the slowest innovator; Chrome is innovative, Firefox is derivative. Sad!