uepselon

This plugin offers your blog visitors a <a href="http://www.foxload.com/firefox-download/" title="firefox download" rel="nofollow ugc">firefox download</a> button in different formats and colors on the sidebar.
Different banner formats and colors are included. The plugin use the wordpress locale settings for proper language versions of firefox.
You can place firefox buttons as widget and if your theme does not support widgets, you can place this <code><?php if(function_exists('get_foxload_button'))get_foxload_button(); ?></code> php code at the preferred position in your template.

Foxload Firefox Download

Offers your blog visitors a firefox download button in different formats and colors on the sidebar.

Minsc

WP LibreJS module provides compatibility with the GNU LibreJS browser plugin.
It adds tags to pages indicating that all JavaScript is GPL v3+. It will only discover JavaScript files as they are loaded by an administrator user, so every time you add new JavaScript links you will have to load a page that have those links, with an administrator user logged in.
Note: you should only install this module if you are sure all JavaScript on your site is in fact GPL v3+ compatible.
WP LibreJS is <a href="https://www.gnu.org/philosophy/free-sw.html" rel="nofollow ugc">free software</a> and it gives you freedom!

WP LibreJS

WP LibreJS module provides compatibility with the GNU LibreJS browser plugin.

Foxload Firefox Download vs WP LibreJS