Core: Fix URL handling in Firefox

[raon0211]

Issue:

When opening a storybook build in a local filesystem with Firefox, an error occurs.

The error indicates that some string like null/Users/raon0211/dev/repo-name/storybook-build/iframe.html was passed to the constructor of the native URL class.

This is because when Firefox parses URLs with protocol file: (e.g. file:///Users/raon0211/dev/repo-name/storybook-build/index.html), the resulting url object has origin "null". (See this bugzilla link.)

As documented in MDN, the origin of URL objects is browser dependent when the url has the file: protocol.

What I did

I used the browser-independent protocol and host instead of origin to fix the problem.

How to test

• Is this testable with Jest or Chromatic screenshots?
• Does this need a new example in the kitchen sink apps?
• Does this need an update to the documentation?

This issue only occurs in Firefox.