"README.dependencies" for gnucash states: webkit webkitgtk-3.0 (Windows, Mac) webkit2gtk-3.0 (Everything Else) For Ubuntu Xenial, this is clearly wrong. webkit2gtk-4.0 is what is needed. Using webkit2gtk-3.0 yields "URL cannot be shown" when clicking on accounts in reports and some other report functions with Gnucash 3.6 Using webkit2gtk-4.0 fixes the problem. See the discussion with this same subject at gnucash-user at gnucash dot org for July 2019.
Testing on Ubuntu-14.04, which provides only libwebkit2gtk-3.0, displays "URL cannot be shown" when following an account back-link. It's supposed to work on Ubuntu-14.04 so the problem isn't README.dependencies, it's in gnc-html-webkit2.c.
Fixed in git for 3.7. When I implemented the WebKit2 interface three years ago I had done the navigation policy--the code that hooks our special account URIs--only for WebKit2Gtk-4.0. I've now implemented that for WebKit2Gtk-3.0.