fix: avoid popup being invisible in Firefox

[dbjorge]

Description of changes

For some time, the extension's popup window has used CSS that sets body, html { height: 0px; } as a workaround for a Chromium issue where, without that CSS, the popup window does not resize like it should when its content is zoomed in/out. It doesn't actually set the window height to 0; it forces it to dynamically fit the content.

(note that, due to a separate Chromium issue, you can't zoom in/out on the popup content directly; to observe this, you need to have the popup open while you're zooming in/out on a different extension page, like the details page)

In Firefox, the original workaround has the effect you would actually expect, and causes the popup window to be of 0 height, ie, invisible. Using fit-content instead of 0px still achieves the desired dynamic zoom behavior in Chrome, but also achieves a correct popup window size in Firefox.

Note that this fix does not allow for correct popup window zooming in Firefox; it only enables correct window sizing in Firefox at the 100% zoom level. Popup window sizing at other zoom levels is broken in Firefox due to Firefox bug 1570849, which appears to affect all extensions that use this type of popup window.

Before:
Firefox:

Chrome:

After:
Firefox:

Chrome:

Pull request checklist

• Addresses an existing issue: Part of Firefox support? #445
• [n/a] Added relevant unit test for your changes. (yarn test)
• [n/a] Verified code coverage for the changes made. Check coverage report at: <rootDir>/test-results/unit/coverage
• Ran precheckin (yarn precheckin)
• (UI changes only) Added screenshots/GIFs to description above
• (UI changes only) Verified usability with NVDA/JAWS