Bug 16444: Update audit process for Firefox ESR

The GENERAL document contains notes about a new procedure for reviewing
new features in Firefox releases for the next ESR Tor Browser will be
based on. The document is named GENERAL as we might want to describe
other parts of the audit process at some point, too, making this a proper
documentation of the audit process itself.

audits/GENERAL

+Motivation
+----------
+
+Preparing the switch to a new Firefox ESR begins usually as soon as it lands on
+Mozilla's beta or release channel. This means for us we have 12 to 18 weeks to
+prepare a Tor Browser release based on it. This includes adapting our Gitian
+setup, rebasing and testing our old patches, auditing the network code,
+reviewing new features and modifying them to fit our needs, testing them in at
+least one alpha release etc.
+
+While there are things that are tricky to do without additional overhead before
+a new ESR got out, reviewing new features, prioritizing them and filing tickets
+is not necessarily one of those.
+
+Feature review process
+----------------------
+
+To illustrate the workflow of the feature review process let's assume we just
+got Tor Browser based on Firefox ESR 38 out of the door. Mozilla released
+Firefox 40 meanwhile. One of the Tor Browser team members is catching up on the
+Firefox for developers documentation for version 39 and 40 and is filing bugs
+with the "ff45-esr" tag. Reviewing the developer documentation and filing
+respective bugs is happening successively after Firefox 41-44 get out as well.
+This procedure is covering the most important and most difficult to patch things
+and should therefore be enough for the first pass. As a bonus point we might
+even get hints about possible problems with code already in the ESR 38 series
+this way which would allow us acting quicker in fixing those issues in our
+stable series.
+
+When we finally start preparations for the switch to ESR 45 we basically have
+all the ff45-esr tickets filed, and ideally prioritized, which are resulting
+out of Firefox 39-44 reviews. The only remaining tasks for the feature review
+are: taking care of ESR 45 and double-checking the undocumented bugs and the
+ones with milestone Firefox39-45.