Firefox Hacks [Electronic resources] نسخه متنی

Hack 22. Edit Configuration Files

Modify configuration files where it makes sense
to do so, and ignore the rest.

Table 1-1 in the introduction to Chapter 1 describes the location of the two important
file areas that Firefox uses: the install area and the profile area.
This hack runs through the files in
those two folders, pointing out which ones can be modified for good
effect and which ones are pointless to modify. If changes are made to
these files using the Firefox GUI, then a restart is rarely required.
If files are changed by hand, as described here, then a full restart
of the browser is almost always required and is always a sensible
policy.

Note that on Windows, the %TMP% directory is
also used. The self-extracting Firefox installer temporarily unpacks
its files into that directory. On Linux, you must untar non-RPM
install bundles by hand to an arbitrary temporary directory before
install. On all operating systems, OS files, or at least desktop
files, are also touched during install.

Many of the following files can be modified with a simple text
editor, although few are designed with that in mind. Of the rest,
mostly binary files, small tools exist that can expose their content.
To get these tools, either compile Firefox [Hack #93] or explore the contents of a
nightly build [Hack #92] .

The preference system [Hack #23]
spans the install and profile areas. It is not discussed in detail
here.

3.2.1. Files in the Install Area

Here is a breakdown of the install-area
subdirectories. A file with a
.xpt suffix is a binary XPIDL type library,
similar in concept to Microsoft ATL type libraries. A
.jar file is an archive in PK-Zip
(.ZIP) format:

chrome

This directory holds all the user-interface content that is part of
Firefox, including skins, themes, locales, packages, and associated
resources. Such content can be present in a JAR file or spread over a
further hierarchy of ordinary package folders. The
installed-chrome.txt file is written by the
installer and registers all bundled chrome packages. This file can be
added to by hand, if a package is also copied in by hand, but beware
of accidental syntax errors. This directory's parent
directory exactly matches the top-level of the
resource: URL scheme.

chrome/overlayinfo

This directory is a set of generated
RDF
files derived from and duplicating all of the
contents.rdf files to be found in the chrome.
There is little reason to touch it. It is regenerated on startup if
it doesn't already exist. It is also regenerated if
the installed-chrome.txt file has been modified
(touched) since the last startup.

components

This directory contains
XPCOM
components bundled with the standard install.
They're not considered part of the core runtime
libraries. master.ini and other odd files belong
to the third-party Full Circle Talkback system that generates
diagnostic information if a critical error occurs.

defaults

This hierarchy holds configuration items that are applied before any
user profile items. The only extension normally contained in here is
the default theme. Note that most preferences in here can be
overridden via user.js in the profile area.

defaults/autoconfig

This directory contains references and scripts that apply to locked
preference files [Hack #29] . Note
that the JavaScript functions defined in
prefcalls.js are the ones available for use in
such locked files. The files in this directory can be modified with a
text editor.

extensions

This directory contains extensions bundled with the standard install.
The default theme, Firefox
(default), is the sole bundled extension. The
files in this directory can be hacked.

greprefs

The Gecko Runtime Engine (GRE) is a
semi-independent part of the Mozilla platform inside Firefox. It has
its own specific preferences and defaults. These can be overridden
normally with user.js.

icons

For Linux/Unix only, this directory contains desktop
XPM icons. The files in this directory can be
modified [Hack #78] .

plugins

This directory contains installed plug-ins. Files can be copied here
by hand. Type the URL about:plugins into the
browser Location bar for more details.

res

This directory contains content required for the proper display of
web pages, such as DTD entity definitions like
  and placeholder images. The files in
this directory can be modified.

searchplugins

This directory contains specs for bundled
search-bar search engines. The files in
this directory can be modified.

uninstall

For Windows only, the files in this directory uninstall Firefox and
record install logs. Don't touch the files in here.

On Linux/Unix only, the
registry file in the install area is the do-nothing
top-level registry of Firefox versions installed at this location.
There can only ever be one version. This file is present only because
there is a similar but more useful file on Windows.

3.2.2. Files in the Profile Area

Here is a breakdown of the
profile
area subdirectories. Any directory named
Profiles or default that is
a sibling of the Firefox (or
firefox) directory is a profile for the Mozilla
Application Suite Version 1.x. Also at that top level is the
operating-system-wide registry.dat
(mozver.dat and appreg on
Linux/Unix) file, which records information about all Mozilla-based
installations on the current host for the current OS user, and all
profiles for that OS user. Inside the Firefox
directory is the profile area proper. Two generated files for
Linux/Unix located here shouldn't be touched.

The profiles proper have random characters in their top-level
directory names. New profiles have eight characters of random digits;
older profiles migrated to the current version have only three
digits. These are
salted directory names, a term borrowed from
cryptography. Since files inside this directory are sometime updated
in response to data delivered over the Web, it is safer if this
directory's name is not publicly known. That reduces
the chance of relatively obscure Trojan horse attacks, although the
jury is out on whether such measures are excessive or not. These
salted names also pose challenges for profile migration [Hack #25] .

The files in the salted directory hold all state (all information
changes) derived from the browser session. All
files can be hacked, except for
.dat files in Mozilla Mdb/Mork formatthey
are in too obscure a format to modify easilyand the
XUL.mfl file, which is a binary cache of
compiled chrome. Modifying the xpti.dat file is
also useless. All files can be deleted and will be regenerated as
empty files the next time the browser starts up. It is unwise to
delete the certificate database [Hack #17] because then Firefox cannot
visit secure websites. The localstore.rdf file
contains the last known positions of all windows and any values
specified with the XUL persist attribute.
compatibility.ini is used as a timestamp flag
for re-registering extensions [Hack #84] . Here are the other folders:

Cache, Cache.Trash

These folders hold the Firefox disk cache of web page content. It is
harmless to delete the cache by hand. Change the location of the
cache with this preference:

browser.cache.disk.parent_directory /* default = path to Cache parent */

chrome/overlayinfo

These folders duplicate the function of the
chrome directory in the install area.
They're used if packages of any kind are installed
in the profile. The sum of the two chrome directories is all the
chrome that Firefox understands, unless clever developers add other
locations to the chrome registry. These folders are also used by
extensions to store content or state information as required.

extensions

This folder contains any extensions installed into the user profile.
When the first user-selected extension is installed, the user is
asked whether to put it in the profile area, where migration is
possible [Hack #10], or in the
install area. All subsequent extensions go into the same place.

Any directories named
ImapMail,
Mail, or News
are installed by Mozilla Mail or
Thunderbird, not Firefox. Extensions can also write files directly
into the topmost profile directory where all the other stateful files
are stored. Aggressively written extensions can modify any
user-accessible file on the local disk and can modify the Windows
Registry on Windows.