Permission popover and bookmarks popover are not accessible with keyboard
Epiphany works quite nicely with the keyboard, since (almost) all UI elements and features have a mnemonic character and/or a keyboard shortcut and/or are accessible by tabbing through them (or with the arrow keys).
But I've found out that I can't access the permission popover in the headerbar (the one shown when clicking the lock in the search bar) and the list of bookmarks shown with the button with any of the methods listed above. They can't have a mnemonic because they only show an icon, I can't tab through them because (Shift+)Tab is taken by the webview to tab through the web page's activable elements, Ctrl+(Shift+)Tab is taken by the tabs list, and there's no actual keyboard shortcut to activate them.
So unfortunately the only solution I see is here to add keyboard shortcuts for those two. The situation with the tabbing being entirely taken is actually quite bad but unfortunately I don't think there is much way to fix it as both webview and tabs tabbing are needed. I don't think the nautilus port to the hdy tabs bar would have this problem though, as it doesn't have a webview or prominent text view (like a text editor), but other apps like Text Editor might encounter similar problem if ported to the hdy tabs bar.