I am several hundred opossums in a trench coat
Making a breaking change to the mobile API also breaks old outdated installations of the app. Websites and their APIs are usually synced, apps not so.
If they were really motivated to stop your method, they could just obfuscate the frontend with webpack and break your scraper every time they make an update.
I suspect that any of the methods proposed here would be prone to a C&D, but IMO the safest legally would probably be the RSS method (not a lawyer though). Reddit’s RSS feeds are public, documented, and available without the need for private APIs, authentication, or an API key, so I don’t see how they could claim that a wrapper is unauthorised/illegal. Documenting their private API however seems like a gray area. Google LLC v. Oracle America, Inc. found that APIs are copyrightable, but this use may constitute fair use.
Is there a reason you’re scraping data rather than attaching a network sniffer/reverse engineering the official apps and documenting the results? Or map the RSS feed to an API? The main thrust behind my comment is that I think scraping is pretty fragile, so I’m interested as to why other options are infeasible.
Their teachable moment is that plagiarism has consequences, and they earned that lesson entirely by themselves.
Mozilla’s next largest source of revenue is subscriptions and advertising (source 2021 financial report), by a wide margin. That “useless shit” is their other revenue, and they’re investing in it because they know they need to diversify revenue to fund Firefox. You’re suggesting they kill it because it’s not their core (unprofitable) business?