[gorhill]

This polyfill is useful if you want your Firefox-based extension to seamlessly run as a Chromium-based extension.

However uBO's code base was primarily that of a Chromium-based extension (it predates Firefox WebExtensions), and Firefox extensions API does not require a polyfill to run Chromium-based extensions.

So roughly I just needed both `chrome` and `browser` references to access the same API, the long term goal being to opportunistically replace all instances of `chrome` with `browser` (I find the later more vendor neutral).