I hate gigantic URLs, but not as much as I hate extensions that want to access my data for all websites.
I've shared instructions for inspecting the source code of a Firefox add-on elsewhere in this discussion:
https://news.ycombinator.com/item?id=22388603
WebExtensions like Neat URL continue to work even if you don't update it. You only have to inspect the extension code once (no developer mode needed) if you are skeptical, and you don't have to update it if you don't want to.