• Enable in Settings → Editor → Font → Enable Font Ligatures
• Select Fira Code as "Font" under Settings → Editor → Font
• Optional extension to disable ligatures in unwanted contexts

• Enable in Settings → Editor → Font → Enable Font Ligatures
• Select Fira Code as "Primary font" under Settings → Editor → Font

Additionally, if a Color Scheme is selected:

• Enable in Settings → Editor → Color Scheme → Color Scheme Font → Enable Font Ligatures
• Select Fira Code as "Primary font" under Settings → Editor → Color Scheme → Color Scheme Font

• Enable in Settings → Editor → Color Scheme → Color Scheme Font → Enable Font Ligatures
• Select Fira Code as "Primary font" under Settings → Editor → Color Scheme → Color Scheme Font → Font

Proper support for ligatures was added in 2016.2 (incl. font compatibility & better performance).

• Enable in Settings → Editor → Colors & Fonts → Font → Enable Font Ligatures
• Select Fira Code as "Primary font" under Settings → Editor → Colors & Fonts → Font → Editor Font

NOTE: Since 2016.3 IntelliJ products come with Fira Code bundled with the editor itself. If you want the latest version of Fira Code, install it separately & restart your editor.

If you see something like that

Open cmd.exe, cd C:\Windows\Fonts and then del every file that looks like FiraCode-Regular_**.ttf. NB these files are invisible if you open Fonts in Explorer

If the files are locked you can use Unlocker. In details you should:

• Install unlocker
• Open cmd.exe as admin (press the Windows key, type cmd and right click on the result to run it as admin)
• subst q: c:\windows\fonts, replace q with any other letter if you already have a unit with that name
• Open unlocker from the start menu, Start Unlocker
• Select any file named FiraCode-Regular_**.ttf from the q unit, select Delete and press Unlock all (you could also try simply closing the applications if you can)
• type subst /D q: inside the command prompt to remove the new unit

Issue: https://youtrack.jetbrains.com/issue/IDEA-159901

This should work for Fira Code 1.102 and IntelliJ products v. 15 and later (IDEA, PhpStorm, PyCharm, RubyMine, WebStorm, AppCode, CLion, DataGrip):

• Create idea.properties file in the configuration directory of your IDE (see where you can locate your configuration directory for your product)
• Add this:

editor.enable.optional.ligatures=true 

• Restart your IDE

NOTE: IDEA support of ligatures is considered experimental. E.g. scroll performance may be very slow. It has been reported here

NOTE: There’s an issue on OS X when Fira Code Light is used instead of Regular weight by default (discussion). To work around that, do not install Light weight at all. (this is fixed in latest 16 EAP) Also, installing TTF as opposed to OTF renders better with IntelliJ on the Mac.

NOTE: For latest EAPs of JetBrains products, that file doesn’t matter without setting preference: Editor→Font→Enable Font Ligatures