This manual is for GNU LibreJS (version 7.21, 21 July 2022).
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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.
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You can install LibreJS directly using a generated librejs.xpi file, or by building it from source (See LibreJS Development Notes).
You can also download it from https://www.gnu.org/software/librejs/ or https://addons.mozilla.org/addon/librejs/, but due to Mozilla’s review process the download isn’t always up to date.
Scripts may be blacklisted or whitelisted through the pop-up menu box.
Whitelisted scripts will always be accepted and blacklisted scripts will always get rejected.
It is important to note that this feature recognizes which scripts are blacklisted and whitelisted based on hash. This means that even a slight difference in a script’s code will cause it to be recognized as a separate script.
LibreJS has a default whitelist of scripts that are known to be free but may not declare their license in a format that LibreJS can understand.
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.
You can manage LibreJS’s preferences either from the extension’s entry in your
browser’s Add-ons Manager page (
about:addons) or by clicking the LibreJS
toolbar icon and then the "Settings..." button on the top right of the popup.
This will open a panel containing a whitelist/blacklist manager and a section
to configure your complaints messages to site owners.
Configure the default subject used in complaint emails.
Configure the default body used in complaint emails.
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The criterion is as follows:
For each function definition:
For the rest of the script, outside of function definitions:
"function" means anything executable that gets a name, including methods.
Allowed primitives exclude:
The machine readable format for license declarations that LibreJS uses has changed in the most recent version. This was necessary in order to not break the asynchronous JS loading model that browsers use. Scripts are now evaluated independent of eachother and strictly as they arrive.
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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:
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
Service workers may cause false positives and false negatives, and
there are multiple ways to disable them. The cleanest way is by
false in the
about:config page of your browser.
LibreJS 7.21 depends on a number of Node.js-based libraries that
can be installed using the
$ npm install acorn-loose jassha browserify $ export PATH=$PATH:./node_modules/.bin
To build the extension run:
$ browserify main_background.js -o bundle.js
To build the extension plus create a .xpi package run:
To build the extension including the automated test suite (see TEST below) run:
$ ./build.sh -t
$ ./build.sh --test
Note: this build.sh script relies on no new source files being created.
To debug LibreJS, visit the special URL
on ‘Enable add-on debugging‘ then ‘Load Temporary Add-on‘. Navigate
to LibreJS’s unpacked source directory and select manifest.json.
Lines 39 and 40 in main_background.js assign two variables
controlling the verbosity of
dbg_print() statements. Make sure
these are set to false before building a release.
An automated test suite runs automatically in its own tab whenever the
extension is loaded as a "Temporary add-on" from
about:debugging. Otherwise (if included in the xpi) it can be
launched from the UI by clicking the "Automated self test..." button.
To launch the test suite from the command line, ensure the xpi package has been built with automated test suite. Then install selenium-webdriver and geckodriver, and ensure the latter is in $PATH:
$ npm install selenium-webdriver geckodriver $ export PATH=$PATH:./node_modules/.bin
Now you can invoke the test with
$ node ./test.js
which will print out a summary of test results.
Optionally you can also test with a chosen seed
$ node ./test.js 12345
To check whether a webpage is LibreJS-compliant from the command line, ensure that the xpi package has been built WITHOUT the automated test suite. Then install selenium-webdriver and geckodriver, and ensure the latter is in $PATH:
$ npm install selenium-webdriver $ npm install geckodriver $ export PATH=$PATH:./node_modules/.bin
Now you can check a webpage for compliance with
$ node ./compliance.js <url>
It will open the url in a headless browser, save a screenshot, and output the compliance check result.
For example, to check the compliance of the FSF homepage, do
$ node ./compliance.js https://fsf.org
The script index.js in ./hash_script generates the default whitelist. Run it with the following command:
node index.js > output
Then, just copy the contents of the file "output" to the appropriate place in main_background.js.
Update the version number in manifest.json.
Make sure debug statements are set to false on lines 39/40 in main_background.js.
Update the version number in docs/version.texi
Then run the build script build.sh.
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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 60. We recommend that you use the latest version of your Mozilla browser. LibreJS has been tested on a GNU/Linux distribution, but it is compatible any operating system as long as you’re using a compatible Mozilla browser.
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