Hey @JollyOrc, thanks for letting us know this is important to you!
So I hit "ctrl-f" and enter the word being referred, to find the comment being referred to. Except I can't, because the search only looks at the current screen.
This really bugs me too, so I'd like to find a good solution that doesn't require us to always load lots of posts the user doesn't intend to read. As @Chris said though, it's tricky. Browsers don't currently give developers any control over the in-page search functionality, so if we want to make something searchable on the page, we have to actually render it on the page.
In the end, I can only strongly urge you to refactor the code displaying the page, make it load fast even with large amounts of text. (maybe keep pictures etc. unloaded until visible?) I mean, it's just text, how big can that be?
We actually already do wait to load most images until they're visible.
Even with just text, this is a difficult performance problem. For a fast computer on a fast connection, loading and rendering 25 or 50 or even 100 posts isn't too big a deal. But for a slow device like a phone, which may have a spotty connection, it could be a long wait and it would be a real battery killer.
When someone clicks a link to the last post in a conversation with hundreds of posts, like this one, we want it to load as quickly as possible so they don't get frustrated or lose interest. So we've made a tradeoff that improves performance, at the expense of making in-page search functionality less useful.
The good news is that there's actually already a discussion underway between web developers and browser makers about adding browser functionality that would make in-page searching possible in scenarios like this one. And there may be other things we can try in the meantime. We'll see what we can come up with.