Scroll position lost when testing locally on Firefox

[hiddenhare]

Using the mdbook crate, version 0.3.7, on Windows 10. There appears to be a scrolling bug on Firefox 75.0. To reproduce:

• Visit the book on the local filesystem using file://.

• From within the book, scroll partway down a page and then click a link to an external URL.

• Use the browser's "back" button to return to the page. The scrolling position will have reset to the top of the page.

The bug doesn't occur on Chrome 81.0, or when browsing the book using HTTP over localhost, or when following links between one page of the book and another.