Facet nice dude, keep me up to date how all this works out, I would love to test it
Okay, then collisions might not be the issue that much, I have like 900 up to 1500 objects how does that run on your system? If that runs smooth or okay, then that is not your issue.
Also try another browser, and also uploading your game, don't run locally. Or try Web-Nod, also faster. In general seems chrome to be the smoothest way to play.
But hen most likely it is rather the redrawing end effects slowing it down a lot. Try not to use any fx... they are also fps hungry -- I know, they are tempting, but don't work on all browsers anyhow... (at least some look pretty ugly in some browsers)
Are you scrolling your map all the time? Maybe you can do map-areas, only scrolling, when you reach the edge of the screen. Since scrolling means all objects have to be positioned and redrawn.