This manual is for GNU LibreJS (version 6.0.6, 20 November 2014).
|• Overview:||General purpose and information.|
|• Disclaimer:||Emphasize what LibreJS does and does not.|
|• Installation:||Installing LibreJS from source.|
|• How to Use:||How to use LibreJS in IceCat.|
|• Free Licenses Detection:||List of licenses detected by LibreJS.|
|• Installation Requirements:||Requirements to build and install LibreJS.|
|• LibreJS Internals:||How LibreJS works under the hood.|
|• Tests:||Test LibreJS and better understand it.|
|• GNU Free Documentation License:||Copying and sharing this documentation.|
If you care about freedom in your computing, and don’t wish to let all and sundry make you run nonfree programs, now you can prevent it by using LibreJS.
You can install LibreJS directly using a generated librejs.xpi file, or by building it from source.
After enabling the Add-on SDK, you should be able to use the
command to build LibreJS from source.
make, a new file, librejs.xpi should be
generated. This is the file that can be installed in a Mozilla browser.
To install the add-on for all users, run:
sudo make install
or as root:
Next time you open a Mozilla-browser as a user of your system, you should be notified that a new add-on (in this case, LibreJS) as been installed and whether to allow it to run or not.
When nonfree/nontrivial code is detected in a page, LibreJS attempts to find a relevant contact link or email for the website you are visiting. In order to do so, it will attempt to visit a few links from the current page (for instance, a link labeled “contact” on the same domain as the current page, …)
LibreJS detects contact pages, email addresses that are likely to be owned by the maintainer of the site, Twitter and identi.ca links, and phone numbers.
After LibreJS detects any of the above, a “Complain” tab will appear on the right of your web browser. When you hover over this tab, a large panel will slide in with the contact information. Ideally, at the top you will find the email address of the maintainer, labeled as the “Email you should use”.
Configure the default subject used in complaint emails.
Configure the default body used in complaint emails.
eval()method, use of square bracket method calls, use of concatenation with certain constructs or method calls, …).
When an external file defines a function, it becomes available to all other external scripts. That is the case if another script defines a function that makes AJAX calls, when an external script loads other scripts dynamically (which in turn could also make AJAX calls, …), or when a script is written with constructs that may do any of these.
For instance, if your page contains the following:
<script src="jquery.js"></script> <script> $.doSomething(); </script>
$.doSomething(); may seem trivial, you will nevertheless
have to add a stylized license comment on your main HTML page because
the external script (in this case jQuery) has been found to define
methods that make AJAX calls.
$.doSomething() might make an AJAX call,
and LibreJS does not check for that. The rule of thumb is that when you
use a library or code that handles AJAX, JSON, JSONP, the loading of
scripts dynamically, you should have license mentions for all your
a case that happens very often with code that uses libraries.
accurate Content-Type in the response from the server. For
example, if you’re using JSON, set it to
This is because LibreJS alters the content of
<script> tags in HTML pages,
the license notice should appear once per page as a comment inside a
<script> tag, before all the code in that script. When the only
onclick), place the license notice in an otherwise empty
<script> at the top of the page. This is sometimes needed when an
external script performs AJAX calls or embeds scripts dynamically, and
When people speak of the “MIT license” they mean either the X11 license or the expat license. Please see which license the code uses, and label it accordingly.
If you are using a free license that isn’t detected by LibreJS and isn’t listed in the previous section, please send a message to firstname.lastname@example.org regarding this license, where code released under this license can be found, and where to find the license text and information.
Many free licenses are listed in this page: http://www.gnu.org/licenses/license-list.html
<head>tag, it includes jQuery
First, you must ensure that the library is free. If the file contains a copyright and a license notice, you won’t need to look any further. But if there’s no mention of the license, or if it’s too brief, you’ll have to look for a COPYING or LICENSE file within the original library’s source package, or on the library’s official website.
This might be the case with an analytics tracker, social media widgets, and code that runs ads. Removing these pieces of code from your site is required to have the rest accepted as free. There are often alternatives to nonfree libraries or to third-party services:
be free. The
@licend lines at the
beginning and end of the stylized comment are necessary to make a clear
statement that the _entire code_ in the file is free. This means that
you must ensure that no nonfree code was carelessly appended at the end
of the file.
<script> tags with on-page code and the inline
Since external files have their own stylized comment, they are
not covered by the notice in the main HTML page. Make sure to identify
all the licenses available. LibreJS will only ensure it matches a
notice of an allowed license once, so the order does not matter, but
the responsibility is on you to make sure all code is under the free
licenses mentioned between
You should make only one
comment in your page, since it pertains to the entire code on page
<script> tags and inline html attributes.
You will need one of the many flavors of the Mozilla browser to use LibreJS. It can be installed on the following:
GNU IceCat, Mozilla Firefox, Trisquel Abrowser, Debian Iceweasel.
LibreJS works on these browsers starting from version 29. We recommend that you use the latest version of your Mozilla browser. LibreJS has been tested extensively on multiple GNU/Linux distributions, but it is compatible any operating system as long as you’re using a compatible Mozilla browser.
LibreJS uses the Mozilla Add-on SDK (Software Development Kit), a set of APIs and tools to create add-ons for Mozilla browsers.
You do not need the Add-on SDK to use LibreJS xpi file or to install it
using the packaged version, but it is required in order to package the
LibreJS source code into an xpi file using
make. If you would like
to run the tests for LibreJS or make changes to the source files, you
will need the Add-on SDK as well. For the “make” command to work
properly, you must have the
cfx command available on your system
from the command line.
The latest tarball for the Add-on SDK is available at:
Instructions on how to get it working are available here:
In order to use
make with LibreJS source, however, it is ideal to
cfx available at all times and for all users.
An easy way to do this is to extract the contents of the tarball and to place the files inside /usr/lib/addon-sdk and then creating a symbolic link in /usr/bin, as follows:
sudo ln -s /usr/lib/addon-sdk/bin/cfx /usr/bin/cfx
cfx command will then be available to all users.
The Add-on SDK is released under the Mozilla Public License 2.0.
LibreJS intercepts HTTP responses and rewrites their contents after
attributes from the page, but instead “deactivates” them by modifying
src attributes on script elements and by
into harmless attributes.
In order to better understand how LibreJS works, you can try to visit these pages with LibreJS installed and enabled and see how they are being processed:
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