The absolute most annoying thing about WH: Load page, go to click on an item, item jumps down the page as the nav menu loads.
Solution: Hide the body content until the entire page is loaded. Yes, it will appear to load slower, but the page will be fully functional as soon as it loads, instead of appearing to load in phases, the first of which is unusable.
On further research, it looks like the web app may use synchronous XMLHttpRequest from the main thread, which causes parts of the page to load after the DOM is ready.