As DonGato pointed out in his review, after deleting an entry with a key-shortcut, nothing is selected in the tree afterward which makes it difficult to continue navigating the list with keys only.
His suggestion was to select the next available entry. I totally agree with his suggestion and added it to the extension. Testing this I found that it helped only a little because the focus was now shifted to the button and you had to manually set the focus back to the tree in order to continue navigating the list.
So I added some extra code to set the focus back to the tree after one of the buttons (edit, remove, insert) was activated (and only if the tree already had the focus).
Key-navigation is now improved and feels much more intuitive.