O'Molloy is one of many examples in the novel of Dublin men who have fallen upon hard times. As soon as Bloom sees him, he thinks what a shame it is that O'Molloy seemed to be such a promising young lawyer and then didn't develop into anything. We get a hint of O'Molloy's difficulties at the end when he asks Crawford for a loan and then becomes sullen when it is refused.
That said, O'Molloy is comfortable amongst the men. He comes across as a reasonable man, and disagrees with Crawford when he tries to heap all his journalistic praise on one journalist: Ignatius Gallaher. O'Molloy argues that there are many fine journalists, and shows his appreciation of oratory when he quotes a line from a contemporary, Seymour Bushe, that nearly makes Dedalus swoon.
Later, in "Cyclops," we again see that he can hold his own with the men. He argues with the citizen about law and history, and seems comfortable in the pub. He doesn't come across as much of a leader though, and when the talk turns against Bloom, he pipes in with wise-cracks just like everyone else. Yet the fact that O'Molloy plays Bloom's lawyer in "Circe," suggests that Bloom imagines him to be more sympathetic than most of the men.