Don't skip installing listeners.

Fix listener installation bug.  To see bug, do:

   - open vimium options page
   - use 'b' to select and go to a bookmark
   - use <alt-LEFT_ARROW> to return to options page
   - vimium key bindings are now *not* installed

Bug was introduced in 28e9c8374bfc7a4fd479dbb958a4a87331fb0857.