Works here in Firefox 19.0 and Chromium 24.0.1312.56 on 64-bit Linux.

I didn't see the GitHub link in Firefox, though, so in case anybody missed it here it is: https://github.com/dreamingofelectricsheep/browserpolis.

Say, how do you plan to add terrain height to the game? At a glance it seems that your engine wasn't built with it in mind. It might warrant a total rewrite to put it in as early as possible since it's such a major feature of how SimCity-type games play and (especially) look.

Edit: I was thinking more about how you'd manage placing Bezier roads over an uneven heightmap.