Hey Jim,
We're actually hoping to make some changes to the bookmarks manager in the future, and this will hopefully be a bit easier with ChromeVox. If you want to delete all bookmarks from the bookmarks manager now though, you can navigate through the interface using Search + Right. Once you pass the Organize dropdown menu, you will reach the first bookmark in your list. If you press Shift plus the Down Arrow, you can highlight and select each row as you move down the list (ChromeVox doesn't currently announce that they are selected, but if you are holding down Shift, they will be selected). Once you have the list of bookmarks selected, then you can press Search + M to pull up the context menu. If you arrow down the context menu, then you will reach the option to Delete. At that point, simply press Enter.
Let me know if this doesn't work for you.
- Laura