

This has been my go-to API testing tool ever since Insomnia started forcing users to sign up with an email just to use the program. They stripped the fully-offline model from it and effectively ruined the whole application.
Also, side note–the Flatpak for Bruno is listed as proprietary, but the official GitHub repo contains the MIT license, and the official repo references the Flatpak in the README, so that makes me assume it’s an official Flatpak. What gives? Does anyone know?
You say you’ve already read Librewolf’s FAQ, so I can skip over what they’ve provided in their response.
The only possible downside I could see would be that your encrypted data is stored on Mozilla servers. Which isn’t a very major downside–it’s properly end-to-end-encrypted. This is mentioned both by Mozilla themselves, as well as in the Librewolf docs. This is the only downside I can see right now, but for the paranoid, it might be worth looking toward the future; who knows, maybe some day, Firefox will randomly decide to disable E2EE for Firefox sync. That could be a potential downside down the road. But I find that to be pretty unrealistic… I honestly can’t see a lot of ways for Mozilla to screw this up.
If the prospect of relying on Mozilla servers still makes you uncomfortable, then you can self-host a sync server, but it’s not exactly a quick setup. They do provide a Docker method of installation, at least. The sync server code is found here, along with installation instructions for self-hosting and how to connect it to Firefox/Librewolf/other derivatives: https://github.com/mozilla-services/syncstorage-rs