MozillaTechnology used in TheMozillaProject was one of the biggest OpenSource projects, behind OpenOffice and Gnome, and much bigger than Linux). Initial information in this page is sourced from the article at http://www.devx.com/DevX/Article/17899/1954?pf=true.
It is said WindowsLonghorn will incorporate technology very similar to things already in MozillaTechnology. Compare:
"contrast" is an apropos word -- these are apples-and-oranges comparisons if I've ever seen them. Gecko vs Avalon? XPCOM and .NET? About the only comparable technologies are XAML and XUL