Jetbrains changed the toolbars in IntelliJ 13.
The Navigate Back & Forward arrows, shown here, used to be in the top toolbar and easily clickable.
Method 1
View > Toolbar
Method 2
Press Shift 2 times > write "toolbar" and click on the "switch button" to change "OFF" in "ON":
The toolbar already contains the "Back" and "Forward" buttons.
Method 1
File > Settings... > Appearance & Behavior > Menus and Toolbars > Main Toolbar > select one row and click on "Add After..." if you want to add a new button (E.g.: if you accidentally removed the Forward button and you want it back)
Method 2
Right click on the toolbar > Customize Menus and Toolbars...
Use the approach that is described in Method 1