The livery editor is the last piece of code from the original iGP launched in 2011 which is unchanged and still requires a plugin to run. The rest of the game has already been converted to HTML5 or WebGL meaning no plugins are required to access them. Most browsers are dropping support for browser plugins, which is why they have stopped working in many modern browsers.
We will rebuild the livery editor in WebGL at some point so that no plugins are required. Until then it will be required to have the Unity Web Player browser plugin installed to run the livery editor.
Download Unity Web Player
Supported Browsers
The Unity Web Player is supported by the following web browsers:
Internet Explorer (Recommended)
Safari
Opera (version 36 and older)
Firefox 32bit (version 52 and older)
Unsupported Browsers
Chrome: As of version 45, Chrome no longer supports the Unity Web Player.
Microsoft Edge: Microsofts new broswer, Edge, does not support the Unity Web Player.
Firefox 64bit
Firefox 32bit: As of Version 53 and newer
Opera (version 37 and newer)
Any browser running on the operating system Windows 8RT or Windows 8.1RT does not support the Unity Web Player
Mobile devices such as Android and iOS devices do not support the Unity Web Player