Firefox

Mozilla Firefox is a free and open-source web browser developed for Windows, OS X, and Linux, with a mobile version for Android, by the Mozilla Foundation.

Activate built-in PDF viewer

Write about:config on the browser URL textbox, click on "I'll be careful, I promise".

Look for the property browser.preferences.inContent and set it as true.

Look for the property pdfjs.disabled and set it as false.

Click on the Edit menu, Preferences, Applications, Portable Document Format and set it as Preview in Firefox.

Restart Firefox

Firefox ESR (Extended Support Release) in Slackware64 14

   1 cd /opt
   2 wget http://ftp.mozilla.org/pub/mozilla.org/firefox/releases/latest-esr/linux-x86_64/en-US/firefox-31.3.0esr.tar.bz2
   3 tar xvif firefox-31.3.0esr.tar.bz2 
   4 mv firefox/ firefox-31.3.0esr
   5 ln -s firefox-31.3.0esr firefox

Install firefox 52.0.2 (patch) for slackware 14.2

   1 wget https://slackbuilds.org/mirror/slackware/slackware-14.2/patches/packages/mozilla-firefox-52.0.2esr-i586-1_slack14.2.txz
   2 upgradepkg mozilla-firefox-52.0.2esr-i586-1_slack14.2.txz