Very simple, from the source:
Lemmy Universal Link Switcher, or LULs for short, scans all links on all websites, and if any link points to a Lemmy instance that is not your main/home instance, it rewrites the link so that it instead points to your main instance.
In essence, any Lemmy link you come across is automatically redirected to your home instance. It’s also easy to customise, you can add/remove instances and prevent it from working on particular sites (or force it to only work on sites you wish).
Can be installed with Tampermonkey or ViolentMonkey (or similar tools).
note: this may also work just fine on mobile browsers that support extensions (and would likely help direct your browser to opening your lemmy app - if you have one - more often), but I haven’t tested this.
Seems like something that should be upstreamed. We’re not on Reddit anymore, the source code is open and contributions get accepted. The need for userscripts has been removed basically
Just being open source is not enough to solve this problem. You would need a record of your “home instance” stored somewhere that all Lemmy instances would always have access to it. Ignoring the security implications of that, you still can’t use browser storage or cookies for that storage. In browsers, those storage mechanisms are restricted to the websites that stored them in the first place. Browser extensions have their own storage, so they don’t have this limitation.
I can’t think of an architectural solution to this problem without a browser extension.
The closest alternative that could be upstreamed is what Mastodon does, which is prompt the user to enter their home instance every time they try to interact with something while not logged in. An upstream solution can never be fully automatic like a browser extension, but this may be “close enough.”
True, I didn’t consider that. This particular instance warrants a user script