I've been reading about Multi-Core support in Firefox. There are outdated https://wiki.mozilla.org/Electrolysis#Status Wiki pages. Which states "Firefox should be Multi-Core aware in 2 years", which is now. So I am wondering if Firefox 4, for the Desktop, is optimized for Multi-Core?
Short answer: No. Firefox doesn't have any specific ways of utilising multi-core, although I imagine that this isn't a significant problem for most usage scenarios these days, it might be more important in the future.
Robert O' Callahan has blogged about this a bit before: http://weblogs.mozillazine.org/roc/archives/2006/12/parallelism_1.html, http://weblogs.mozillazine.org/roc/archives/2007/09/parallel_dom_ac.html
Or I recommend the WaterFox Project (Firefox with MMX, SSE2 and x64 favoring enabled)
More news, if any, will be found here: https://wiki.mozilla.org/Firefox/Roadmap