I was wondering what was on top of the fuses on this pole. I see quite a lot of these poles in CMP and Emera service areas.

Are they current transformers? Designed so the power company can  quickly check the amps on the line

These fuses have two parts: The filament wire and the cutout contact.
The filament wire pull is holding the contact mechanism closed. Once the current exceeds the limit, filament breaks so the contact gets released and cuts out the power, swinging the fuse body down.
The top thing is then the arc quenching thing - to help quench the arc that forms when the contact disengages and so break the circuit.
Plus the spring loaded release mechanism is there as well (a latch gets released when the fuse wire looses tension due to its breakage, the spring then "shoots out" the top contact down, all that to speed up the disconnect).

This (the video of the 110kV thing) is not arcing on a switch, but an isolation disconnect. The switch is inside of the horizontal isolator like things, first the switch are suppose to break the load current and then the main arms disconnect all that in a visible manner. The disconnect is designed to operate only with no current, so has no arc quenching, it is tgere just as an extra safety addon.
But here one of them failed (there are two in series), the second half gets an overvoltate so keeps arcing over, then the disconnect starts to operate with load (it is not designed for that), so the spectacular arcing (the load here is some phase compensation bank, if I undestood well, so not that huge load).