I have now gotten things to run using the bits built from this effort (including the xulrunner binary it built) and the latest version from the http://conkeror.org/ git. It is slow as molasses for some reason I have yet to identify (top showed it taking up to 90% or more CPU at times) even though it should be an optimized build. And there are definitely bugs. But at least I know that Firefox 24.8.1 DOES run on the Nokia N900.