@CoolKevin yeah, forcing reload indeed gets rid of the error. It's necessary to open in new tab first to be able to reload, though.
i couldn't really figre out why you are able to see this, but~Full attachments, available otherwise as thumbnails, show "This attachment cannot be shown at this time. Please try back later.", while site can be otherwise browsed normally. This can be seen for example in https://www.akiba-online.com/threads/pb-yuka-ogura-erotikusu-2018-03-23-91p.1810244/ - while attached full image of cover is viewable without problems, clicking on thumbnails below always shows the first photo (the cover); clicking on further thumbs at the bottom of the gallery simply removes them from this view. Opening any of these images in new tab shows said error message.
Can confirm, on Firefox 63.0 all FJ links are missing as of today (were fine yesterday). FJ links present via Chrome 69.0.3497.100 just fine, which is weird since FF has not updated for several days at least.
Can confirm, all Filejoker links have disappeared in Firefox based browsers on my end.
akiba-online.com##a[href^="https://filejoker.net/"]