It's not just the size of content filters. V2 had the ability to run code to block a web request before it was downloaded. V3 only gives you a (size-limited) set of declarative filters. If you want to block anything else, you'll have to do it after it has been downloaded already.

(all here is iiuc; I've never used any of these)

https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/Web...