This also stops the content scripts from being injected into each frame
on reload (in Firefox only). They do not successfully connect to the
background page, and it causes considerable lag, so we lose nothing by
doing this.

Updating URLs to use HTTPS provides greater privacy and reduces the
potential of having content modified whilst in transit (as it happening
more and more by ISPs, networks, state actors etc).

These URLs themselves have been tested and confirmed to work over HTTPS.

The problem is that Firefox balks at function properties within the
response sent via `postMessage` (whereas Chrome does not).

A concise and safe way to sanitize the response is to convert it to JSON
and back.

Fixes #2576.

This stops |Exclusions| from holding a reference to the |value|
parameter passed to |Settings.set|. In Firefox, this object is garbage
collected when the owning context (the exclusions popup) is closed.

The fix for all such cases in the future is to switch to using
|Settings.get|, which implicitly does |JSON.parse JSON.stringify value|
and thus returns an object in the same context as |Settings|.

We could fix this generally by doing this for the
|Settings.performPostUpdateHook| call in |Settings.set| instead.
However, I'm not convinced that it warrants the overhead of a
|JSON.parse| for every |Settings.set| call.

Firefox baulks at "about:newtab" in createTab (but seems happy with no
URL specified).  Chrome is also happy with no URL specified.

(Does this mean that we don't need "about:newtab" ANYWHERE in the code
base?  Could Settings.defaults.newTabUrl just be ""?)

Mention @mrmr1993.

This causes `o`/`O` to crash (producing no suggestions).

As a workaround, set any such title to "".

Improve firefox support