Waterfox is a 64-bits browser, derived from Firefox, and developed by Alex Kontos. It runs great on Linux Mint. Here's how to install it.

Option 1: Install as a portable application

• Download the .tar.bz2 from this page.
• Find the downloaded file in your Downloads directory. Doubleclick on it to start extracting it. Choose the option to keep directory structure intact.
• Extract it to a place where you can find it again; many people would say that the home directory is a good place, others prefer /user/local/bin.
• You should now have a directory named waterfox in your chosen directory; inside that, there's an executable also named waterfox. Doubleclicking that executable file should start the browser.
• To make a launcher for easy starting, just right-click your desktop, select 'create new launcher' and browse to the waterfox directory and the waterfox file, give your launcher a name (Waterfox comes to mind) and click OK. LM Cinnamon will now ask you if you also want it added to your main menu.
• If you want to make your launcher look pretty, an icon file can be found in /waterfox/browser/chrome/icons/default/.
• Once installed, Waterfox will keep itself updated.

Option 2: Install from a PPA

• If you prefer to install from a PPA, OpenSuse has you covered. Go here and follow the instructions.
• Make sure to use the correct version for your Linux Mint version:
  Linux Mint 19.x = Ubuntu 18.04 Bionic
  Linux Mint 18.x = Ubuntu 16.04 Xenial