Garmin has replaced Mapsource with Basecamp as the default mapbrowser. It has improved features like 3D (not available on Openfietsmap, choose in Map Views 2D map - Ctrl+2), better track management, filtering road or waypoint types and better elevation profiles. However, routing is only compatible with the latest GPS devices (Etrex 10/20/30, Montana, GPSmap62, Oregon x50). For other devices, Mapsource is recommended.

Display settings

• 2D instead of 3D view:
  
  
  

• View > Basic Map Only (Ctrl-G) must be turned off
• Utilities > Options > Activity Profile > Map display features : all Line Elements ON
  

Navigation

In the menu Utilities-Options (Ctr+O) > Add Activity Profile:

Add Activity Name: OFM
Activity Type: Automotive or Driving (v.4.1)*

Routepreference:

• Shorter Distance
• Faster time (prefers cycleways and -routes)
  

Road Type Avoidances:

• Never avoid major highways because the cycleways are the major highways!
• Residential roads: avoid footways/forest trails
  
• Unpaved roads are also gravel compacted bikepaths

Feature Type Avoidances: 

• Nothing selected (except cable cars/climbing paths);
• Toll road avoidance will prefer routing on bicycle routes,
  
• carpool lanes avoidance will avoid all unpaved, gravel bike- and footpaths and steps
  

*) In the activitiy types Bicycling/Tour cycling carpool lanes are automatically avoided, which means in OFM this avoids unpaved/gravel bikepaths. Also Toll road avoidance is not available in this profile.
Acctivity type Walking will ignore oneway streets which can be useful in cities. Hiking will do the same but here are Interstates/Major highways selected and greyed out (interstates/major highways are cycleways and -routes on OFM)