If you experience a "crash on start" as you open the webpage at play.civsync.com and all you see is just a blank frame with no game running in it, then there is a possibility that the fault isn't caused by an actual software bug, but that instead your browser misses the required plugin to handle the game applet. In fact, fewer and fewer browsers for desktop computers come with a pre-installed Java plugin, which is required for running Freeciv-web.
You can take a quick test to see if you have Java installed, by going to civland.org/chat and see if the chat Java applet boots up as you open the page. If that doesn't work too, then very likely your browser misses Java and you have to install it from Java.com.
If you have a different issue by the form of a "crash on start", drop a message below and someone will look at it.