In a bug report titled ‘Onebox uses wrong URL for the favicon in link preview,’ JoshuaH observes that Discourse’s onebox feature incorrectly constructs favicon URLs for link previews by appending ‘/favicon.ico’ to the full page URL, rather than respecting the actual favicon path specified in the page’s HTML (e.g., https://invantive.com/favicon.ico). This results in broken or missing favicon images in previews, as seen on https://invantive.com/products/invantive-control-for-excel.html. IAmGav initially thought it was working, but after clarification from JoshuaH, acknowledged the issue here. JoshuaH notes that in some cases, the preview omits the favicon entirely instead of showing a broken image, suggesting inconsistent behavior. The core problem is that onebox does not parse or respect the <link rel="shortcut icon"> tag, instead making a naive assumption about favicon location based on the page URL. This misbehavior affects visual consistency in link previews and may confuse users or diminish perceived site credibility.
But it uses the favicon as the little image next to the title:
This works for invantive.com, since it takes that URL and adds ‘/favicon.ico’ to the URL, which is the correct URL.
However for the other example, it creates the favicon URL by using the link URL and adding ‘/favicon.ico’, which isn’t the favicon URL used on that page (it’s 'https://invantive.com/favicon.ico' on that page too) and thus creating a broken image.
But strangely enough, it seems in your preview it doesn’t show the broken image anymore, but no image at all, not sure why it chose to entirely ignore the favicon.
Happened just a few minutes after my screenshot, where you can see there’s a missing image (there’s some empty space before the title in my screenshot).
