I have not changed any accessibility settings but I reviewed them to be sure. I tried turning on the Mini Toolbar but that just made things smaller and corrupted the favicons while the focus was still on the settings window. The corruption cleared once I returned focus to the main window.

I'm not sure what you mean about a top-border in Safari. I tried quiting any extra apps like Bartender and Better Display but it made no difference.
I've tried a number of browsers on my Mac: Safari, Chrome, Edge, and Firefox. Orion is the only browser I've tried that has this problem with favicons being too small. I'd really like to address this issue since I otherwise am quite enjoying using Orion.