So, 5 years later (or more), Flarum still has this problem where navigation through mentions or unread posts is unreliable if there are unloaded images on the site. When loaded, the images expand, messing up the height of the scroll, showing you the incorrect post. This makes the usage frustrating because links to certain posts lose meaning if they only lead you to a post nearby.
Now, I have seen on the Github issues page that a guy recommended a library to help remedy this problem - however, I have not figured out how to use them to remedy the problem. The post on the issues page I'm talking about is this:
I'm guessing you'd import this and create an extension that applies it for all the <img> elements? I'd appreciate it if there is someone who can help me tackle this problem, it's very frustrating >.<