I've never configured my cache in Firefox. Just looked at the settings, and, as far as I get what's written (it's not very clear), there's no limit at all on my cache size.
Chrome has several different caches (HTTP, DNS, SSL session data, etc.) but looking at just the on disk HTTP cache my laptop is currently using 201MB with the default settings. For anyone else who is interested, you can see the cache stats at chrome://net-internals/#httpCache
It's currently using 350MB.