Be aware that removing the supply ground/earth connection to the oscilloscope (called "floating" the 'scope) can be dangerous to you and shorten the life of your 'scope.
I had a bad shock once using a 'scope I had recently bought. The previous owner had floated it and I did not check the plug. All I touched was the probe socket!
Lots of people do it this way, but I don't.
Alternatives:
1. A differential/isolated 'scope probe.
2. A battery-powered 'scope.
3. Run the 'scope from a battery and inverter.
4. Use both channels, in channel differential mode. Just connect the center tips to the circuit, not the grounds. This has limited bandwidth and excess noise, but is often useful.
If you float, be careful and remember to reconnect the earth when you are finished.
Cheers,
FoxyRick.