Not much. The former was a mainly ethnic and religious medium-intensity conflict in which the bone of contention was whether or not Ulster should secede.

The latter were a period of vast tensions and unrest of an exclusively political nature, with the more extreme wings of the left and right engaging in political violence and terrorism. The goal was the establishment of a fascist or communist dictatorship in Italy.

Obviously when you decide to take up arms you do so in the same way whatever your reason, but other than that there are not many possible comparisons. It is interesting, however, that the foreign backers are in many cases the same: for example the IRA separatists were in contact with Middle Eastern and Soviet bloc states in exactly the same way as the Italian left-wing extremists