The problem with all vim-style extensions is that they have been limited in potential functionality. For instance they won't work in any builtin pages such as about: pages or the new tab page or https://add-ons.mozilla.com. This forces the user to think about whether their command will work or not and induces an uncertainty in their flow.
The other issues regarding limited control over the browsing experience may be resolved with future API expansion, but the previously mentioned hobbling is something with which we are most likely permanently stuck.
The other issues regarding limited control over the browsing experience may be resolved with future API expansion, but the previously mentioned hobbling is something with which we are most likely permanently stuck.