Historically, those areas and their smaller-dwelling neighbours were the Dublin heartland of Fianna Fáil and, to a lesser extent of popularity, Labour. The stereotype was of the tenement resident rehoused in the suburbs, perhaps even purchasing his house from the Corporation, thanks to Fianna Fáil benevolence. They responded to their social franchisement with gratitude. Maurice Manning quotes a late 1960s survey that put party support in Dublin at 35/30/20/15 (DK/Others) among the middle class, and 37/14/31/18 among the working class. My judgement is that you should move about 10% from Others to Fine Gael to get more realistic figures. But the point is that Fianna Fáil was the most popular party among workers at the time.
And remained so, particularly on the northern working/lower middle-class fringes of Dublin city (this was Haughey country before it became Ahern country), right up to the moment when FF fell into the abyss in 2008. The corresponding areas on the southside (e.g. Crumlin) were never as strong for FF.
