[CONTENT-CHANGE] add: arkenfox user.js for Firefox

[atomGit]

the arkenfox user.js project is an extremely comprehensive, privacy-centric user.js (custom preferences) for Firefox in that it alters nearly 300 preferences

this is a very serious project that would be of interest to anyone concerned about browser privacy and security

the project also includes scripts for updating and cleaning a user.js, as well as a reasonably comprehensive wiki with lots of valuable info

there are over a dozen contributors and many of them are very knowledgeable with connections to Mozilla and the Tor project

this project/user.js is not for the faint of heart - i would say that a moderate degree of technical understanding regarding Firefox is required, as well as the diligence to keep the user.js updated - the benefit is a 'quieter' and a privacy and security hardened Firefox

i'm not sure where this would fit best - perhaps in 5_Privacy_Respecting_Software.md or possibly in the How-To Guides section under 'Software'

personally i think the latter would be the better choice

edit: content was edited to reflect the new name of the project - 'ghacks' was replaced with 'arkenfox'