Well, that's hard to say. The first thing I'd do is to enlist Chrome to help me find out.
If you click on 'take a snapshot' chrome will look through your project and provide you a list of what is using how much memory. A lot of that is going to be difficult to decipher but what you'll be looking for is really large numbers on the right hand side under 'retained size.' If you start expanding out the tree looking at what's consuming the most memory, you may... I say may... be able to recognize some of the data in there and spot the problem.
You can also select the performance tab at the top, click on the memory checkbox, and record your session. One of the graphs will be of memory and at the top will be screenshots of where you were in the game. If you see a huge spike in the memory, look at the screenshot to see what was happening and that may help you zero in on the problem.
One other thing to check if you use local storage, select the application tab at the top and then select 'clear storage'. You'll see a pie chart that will tell you how much memory local storage is using.... and guess what, local storage has a huge limit (30gb on my system with 32gb ram). You can browse through the local storage tree below that. Start looking under 'IndexedDB' and look for LOTS of key/value pairs.
I can say with little doubt that it's likely somewhere in your code and not C3. While I've been writing this, my latest project has been running in the background and it's staying at a pretty solid 42mb.