Do aircraft ever dump extra fuel before landing?

No jettisoning unless an emergency requiring it -
Further, airlines have policies "to dump or not to dump" -
Some airplanes do not have a jettison system, so they are required to fly and burn the extra fuel -
Fuel jettison system is often an option, especially for short range airplanes -

Note that all airplanes are "flight tested" for landing at their maximum weight (by test pilots) -
But they have a "maximum landing weight" which is more conservative -

As pilot, I personally did prefer to save fuel and avoid fuel jettison -
The only valid reason would be certain emergencies, or landing on short runways -

I once landed a 707 cargo which was near maximum takeoff weight -
We called operations, and told them we could not retract one main landing gear -
I asked what they wanted me to do - they answered "land as is" -

Maintenance fixed the landing gear that we could not retract -
The overweight landing inspection took but only 30 minutes...!

Several years ago, my wife and I were on a DC-10, departing from LAX for HNL. Shortly after takeoff we were just passed Santa Catalina Island and a baggage door warning light came on. We dumped fuel and returned to LAX. It took about an hour to replace the door and refuel. We didn't deplane. It was interesting though, a maintence man removed a hatch next to my seat and was able to look through the lower deck and watch the crew replace the door. When we took off about an hour and a half behind schedule, the 5 hours to HNL was without further incident.

NO: fuel is very expensive so isnt dumped unless there is a very real risk of fire

Mostly not since it is all calculated (fuel expenditure etc) but if the plan takes of and has to land in an emergency where not a lot of the fuel has been burnt it would dump fuel as it would be too heavy to land which risks damage of airplane gear

if there is an emergency landing soon after take off, or before reaching the destination, the fuel might take the plane over the safe landing weight and so they would have to dump fuel before landing.

Hmm! Yup (waste huh?)