Molior RS takes place in Geilinor, during the early 5th age, year 20 (5e20). Exactly one year after the attack of Delrith, during the reformation of the Void Knights, and just 3 years before the defeat of Northern Morytania.

Here's a full detail page from Runescape.wikia on the lore:

All the events that have happened in Runescape's lore are the same as in Molior, just expanded upon. For example, Crandor in Runescape is a ruin due to the dragon Elvarg who destroyed it in year 5e139, (roughly 30 years before current day Runescape) but in Molior RS Crandor is a thriving trading port, with its own story-line and may explore-able areas.

Another example is the Runecrafting Crusades by the Fremennik. They are 'viking barbarians' who believe runecrafting should be left to the gods, and in 5e42-5e62 they took over a large area of land between Varrock and Falador which in Runescape is known as "Gunnarsgrun" or more commonly known as the Barbarian Village. In Molior RS that has not happened yet. Which also means that the Dwarven city of Camdozaal is not yet in ruins (and is a playable area much like Crandor) in Molior RS.