There is a growing market for privacy (confidentiality), in my amateur opinion; at least it seems that many consumers choose privacy when given the option and they dislike surveillance.

Why doesn't Mozilla heavily promote Firefox as the 'private' browser, and why not focus on enhancing those features, instead of leaving it to others to make the 'private' browsers by modifying Firefox?

1) Otherwise browsers are functionally the same for consumers, ignoring trendiness and user familiarity. Some browsers may do certain things milliseconds faster, or more often be perceived to perform faster, but there is little practical difference besides confidentiality. (I realize this may be controversial to some, but I doubt choice of browser impacts most people's productivity beyond confidentiality issues.)

2) Other browser vendors could not easily compete with Mozilla in the area of confidentiality: Their business models often include tracking consumer behavior, and their brands are not as trusted to put users first as a public interest organization is (and it depends on trust; consumers can't verify these things themselves).

3) Other browser vendors would be forced to try to compete regardless and improve confidentiality, and awareness of and demand for confidentiality would be increased, furthering Mozilla's missions. I think demand for confidentiality often is overlooked because consumers rarely have the opportunity to express it -- it's hardly ever an option.

Regarding the features: Not all confidentiality features are suited for general use (e.g., NoScript), but many are and some could be options for more advanced users. For example, why isn't there a Tor button or pref in Mozilla's official Firefox releases, which connects to Tor and routes all traffic through it? IME, it works fine, though a little more slowly, for most purposes.

EDIT: A few additions and clarifications.