EWR-ZRH is one of the United Operated flights into EWR, it will always arrive into Terminal B (Until at least 3/25)
That said, its 1:40pm arrival time is a moderately busy time for International Arrivals into Terminal B. I would say 15-45 minutes for those holding a US Passport, 30-90 for those who do not. Should you get pulled aside for secondary, expect 2-3 hours, at least.
After exiting customs and immigration, turn left, drop your bags (so long as they are tagged to MFR - otherwise the airline services desk will be right there to print a new tag)
Your EWR-SFO flight, appears to be flight 1143, which is operated by Continental, and will leave from Terminal C. After dropping your bags, continue straight to the elevator/escalator and go up one level. Walk across the concourse, and take the AirTrain to Terminal C. (Time from exiting Customs to AirTrain is 5-10 minutes)
Exit the AirTrain, and proceed through security (Time on AirTrain will be 5-10 minutes, inclusive of waiting for the train)
You will be at the C-2 checkpoint, which can get busy because its right by the AirTrain, if the line looks long, try C-3 (accessible through a walkway from C-2 or C-3, which requires you to go up one level, and back
down. -- All 3 have Premier Access lines (located to the right as you look at the checkpoint). (Figure on 15 minutes for Security)
Best case, this connection will take just about an hour (from landing, to boarding).... However it could take well in excess of double that time. There are two more flights to SFO, that will get you to MFR later that day (12:10am)