Reproduction steps:

1. Create a New Project
2. Switch Build target to WebGL
3. Switch Scripting Runtime to .NET 4.6
4. Build And Run
5. Change the Resolution in the Player Settings
6. Build And Run

Expected Result: The Build opens in the browser with the new Resolution settings
Actual Result: The browser opens a tab, but fails to open the build***

Fixed in: 2018.3.0a1

Reproduced with: 2018.2.4f1, 2018.1.9f1, 2018.1.0a7, 2018.1.0a6, 2018.1.0a1, 2017.4.9f1, 2017.4.2f2, 2017.4.1f1, 2017.3.2f1, 2017.2.2p3, 2017.1.3p3
Did not reproduce on: 2018.2.0a7, 2018.1.0b13, 2018.1.0b1

Note:
Only reproduces on .NET 4.6 and Windows (Tested on Windows 10 Pro)

***
"This site can’t be reached
localhost refused to connect."