You must be using a browser which can support Unity Web Player plugin to access the livery editor. To be honest, I'm not sure which browsers support the plugin anymore.
Edit:
Found a list here. Take a look.
If none of that makes any sense to you, it's technical stuff. You might remember plugins like Flash and Java in the browser, well they all got blocked by the major browser vendors in recent years and we've had to redevelop the game to use WebGL as a result, which is not a plugin.
We will rebuild the livery editor in WebGL at some point so that no plugins are required. This is the last piece of code from the old game (the original iGP launched in 2011) which still requires a plugin to run. The rest of the game has already been converted meaning you don't need plugins to access the live race or the rest of the interfaces.
Guest
CEO & CTO