There's addons/extension for Chrome and Firefox. Both also called JSON Viewer (different author).
For really large files I use a command-line tool plus grep and awk though https://stedolan.github.io/jq/
jq looks promising but I still need to view the JSON file first. I want to be able to somehow get the general understanding of the structure very quickly and interactively. The tree control works very well for that. JSON Viewer is almost perfect but it doesn't work with local files.
I usually use jq to understand the structure of the file. `keys` will get you all the key names in an object; `with_entries(.value |= type)` will replace each element on an object with its type. You can quickly delve into a JSON and gain some understanding of it with jq.