As far as I know, actually, trolls are usually lumped in with jotun-kind. (The ugliest among them, as they are usually described.) And I've personally never heard mention of the term "goblin" in any Norse saga.
The Sagas are no longer the entirety of the mythology.
There is also myths from various countries once dominated by the Norse, such as the Orkney Islands, from where the term "Trow" comes from.
Trolls may be the equivalent of giants, but are also often smaller in size.
Then there are the Vitterfolk, which are human-sized (huldrfolk, etc).
Once we hit the era of the fairy stories trolls range in size from that of giants to as small as dwarves.
Elfquest in fact blurs the line between Dwarf and Troll IIRC.
As for goblins, that is technically a French or Anglo-Norman term IIRC, but I have run across some comments as to the nature of orcneas (Beowulf). They are not defined, but the translations I have found seem to distinguish them from giants. In my own mind they become something similar but smaller, possibly "Hell-corpses" as defined by another analysis I ran across. It is from Tolkien for one where the terms Orcneas (orc) and goblin cross and often become one.
Remember that "spirit", "jinn", "demon", "fairy" and even "goblin" have dual-purpose in that they can mean a generic or a specific and that their meanings can cross unless one is speaking purely in terms of a specific resource (like a specific story, such as a saga or the Dresden Files, but even then sometimes terminology "evolves" (like we see in Tolkien)).