I thought the Dominion was the name of the government but the Thalmor described the ideology and their stealthy actions. That's how I've read it but I guess I could be mistaken.
In reference to the historical Aldmeri Dominion of the second era, the pocket guides present the Dominion as the name of the country, and Thalmor was the name of the regime. It's the difference between the United Kingdom and Parliament. I think the ideology aspect might be more consistent with the Thalmor as presented in MK's gifts to the community, but MK's Thalmor strikes me as the more modern Thalmor rather than their historical predecessors.
Hmm, to be honest I'm drawing my usage from the Pocket Guides, not from Infernal City in regards to the new state of affairs. And the Pocket Guides are certainly not infallible sources.
Thalmor of the pocket guides != Thalmor of the Infernal City. They might have similar ideologies or practices, but their different entities. There's a whole era separating them.
@Hairdo, I'm checking the book right now for how Dominion/Thalmor are used in reference to the new state. I don't have a Ctrl+F for the book though, so I'll get back to you guys in an hour or so.
edit2: page 152, chapter 7:
When one of their agents in a local Thalmor nest reported it, he easily backtracked the leak to a mid-level official who was apparently hemorrhaging information to a mistress who was-as it turned out-a Thalmor sympathizer.
This is from a segment that follows Colin. It talks about the Thalmor like it's a terrorist group.
Page 154, Titus Mede refers to the Thalmor as "our quiet enemies." They apparently fund a gang that likes to decapitate people called the "natives."
Page 154, Colin's training focus is the Thalmor.
Page 154 again, Colin claims their (Thalmor) goal is to bring about a new Merethic era and the pacification and purification of Tamriel.
Page 154, The thalmor "put the old Aldmeri Dominion back together."
It looks to me that the Thalmor are, as a unit, operating in a Hamas/Hezbollah like organization that both operates as a terrorist group and the ruling entity in their state, which seems to be the Aldmeri Dominion again. However, it's notable that no one really talks about the Dominion, it's all about the Thalmor.