User Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:52.0) Gecko/20100101 Firefox/52.0 Build ID: 20100101 Steps to reproduce: As a result of [bug 1413413](https://bugzilla.mozilla.org/show_bug.cgi?id=1413413), a `*.js` file located in a `/profile/preferences/` directory can no longer override `profile/user.js`. Having this ability made it easy to use and keep up-to-date with a third-party `user.js` file while making necessary modifications. [Please see here](https://github.com/ghacksuserjs/ghacks-user.js/wiki/1.5-Keeping-Up-To-Date). In addition, it makes it easy to create relaxed or hardened rule sets without creating a new branch of your profile. Proposed solution: Extensions are denied access, but allow users to place files in `/profile/preferences/` with read properties that are only allowed during startup.

The code that implements this functionality has been removed. After sending an intent to remove email to dev.platform and discussing, we decided that it wasn't worth the effort of continuing to support as we re-implement the preference service.