I have noticed the problem isn't exclusive to thumbnail images either. Well that solution doesn't even seem to work like it used to anymore recently. It was working for a while as a half assed fix, since it's annoying to do this often instead of a solid fix for the problem instead. What I was doing to somewhat bypass this problem for a while is holding down shift and clicking refresh. I've also noticed the issue when opening threads, a few thumbnail images might load, while others will be missing and load after a while or they'll never load no matter how long I leave it there. Nearly every time I check the catalog if I'm lucky, I'll see maybe 10-15 thread thumbnails and the rest will be unloaded with a rare chance of the webpage finally loading those missing thumbnails after waiting 5-10 seconds, but this doesn't do it for the whole webpage of missing thumbnail images. With the main problem website, it's very strange because I'll go to the catalog that'll have the one page show all the threads and thumbnails attached to click on. I'll run into odd issues where thumbnail images won't load on websites like 4chan mainly, but less commonly gelbooru will have a hiccup on some pages, causing me to refresh for it to properly load images. My problem is that when browsing around on some websites on firefox. After some testing though, I doubt that's the source of this issue. I've ran into a really weird problem recently and originally I thought it was because of our new internet service plan upgrade, which came with a new modem/router in one device.

Firefox stuck in safe mode