'65 or '68, the point still stands.
As for opening fire on those throwing petrol bombs, I'm not so sure your police would open fire with normal rounds unless they were cornered or trapped. Generally, if you look at the Northern Ireland riots, or the race riots here in the '80s, there tended to be a hard core of petrol bomb throwing tards with a larger crowd of demonstrators (maybe throwing rocks etc). British police tended to use rubber bullets and tear gas - less collateral damage. I think American riot police would also try and limit loss of life.