The hamburger menu, for one. It's extremely unintuitive. Not the fact that it uses a hamburger icon, but that even simple things like accessing the full list of my bookmarks involve multiple clicks. If you know the keyboard shortcuts then it's not a problem, but I want common UI items to be accessible from the UI.
Besides that, the UI is just sluggish a lot of the time. It feels that Chrome(ium) has a far better latency response.
In both cases you get a list of bookmarks on step 2 and you get a full, searchable, editable view in step 3. The global shortcut for the third step is the same in both (ctrl + shift + o).
I can't imagine why you would say this. Could you point out some concrete examples of better UX?