Minecraft Modder and software developer.
Well, it’s actually a bit simpler than that.
You can directly browse a community that technically lives on another instance without ever leaving your instance.
If you’re on the start page of your instance you can e.g. change between seeing Local, Subscribed or posts from all communities (across instances).
You can click around and browse from there without having to leave your instance :)
I recently noticed that this is actually a bug that’s been fixed four days ago (Github).
Until your instance of Lemmy updates, you’ll have to open the post or comment on the original instance using the rainbow button above the comment. GIFs already work on the same site that you post them on.
After a little of investigating it seems that Lemmy currently unintentionally blocks video files from loading from different sites.
That means that only GIFs (internally handled as mp4 I think) from the same site will load correctly right now.
A fix for this has apparently been implemented 4 days ago, so it just depends on when the fix is officially released (currently in beta for version 0.18) and when your instance updates.
Until then, you’ll just have to open the comments or posts on their original site.
Interestingly enough, right-clicking to open the image in a new tab seems to work 🤔 (Firefox 114)
Iirc it was mostly about storing some user preferences and providing push notifications.
Reddit apparently has no async API for notifications, so 3rd party apps are forced to regular polling.