Congrats on getting your project to the front page of HN. With that said I think you are going to need to change your approach if you want this project to be usable as more than a toy project in the long run.

From what I can tell it essentially saves a map of url -> response in memory as you browse. Every 10 seconds this file is serialized to json and dumped to a cache.json file. This is going to be very inefficient as the number of web pages indexed grows since you are rewriting the entire cache every 10 seconds even if only a few pages have been added to it. It also will eventually exceed the memory of the computer running the app if the content of every page ever visited needs to be loaded into memory. I highly recommend looking into some of the other suggestions mentioned here, either sqlite or mapping a local directory structure to your caching strategy so that you can easily query a given url without keeping the entire cache in memory, and also add / update urls without rewriting the entire cache.