Yep if you're willing to trade weight you can easily get a core i7-3840QM which can do 8 threads (4 cores) fairly fast. My current one I've been able to emulate some of the last gen consoles even for fun, compiling Firefox or Firefox OS is largely going to be an issue of disk speed which is fixable with either gobs of ram or and SSD, (preferably both, though overprices the alienware m18x r2 will take multiple drives, an msata ssd, and 32gb of ram and can be upgraded to workstation graphics cards if you have the cash).
When i was last using gentoo (which admittidly was a while ago) it was pretty much the bottle neck for most things if you wanted to compile in parallel, largely because intermediate steps are written out to the disk before linking and less so because of reading. That said it is possible to do it all in memory but then you end up memory bound which is also possible to work around by throwing money at your ram (or downloading more off the web).
Not a bad idea, all of mine is speced from about 1.5 years ago before haswell was publicly available. So while a little dated, certainly more than enough to do pretty much most of what someone wants.
