Simple and adequate, great work!
It could be even faster, adding a button to update the specified bookmark with a single click. And would you consider adding an option to update the bookmark name to the current tab title via a different button? Thanks!

EDIT: Raised to 5 stars, now works exactly as needed!

New changes are welcome. I think other than double clicking to website adress a select button will help updating better. Also after selecting new bookmark there can be a better confirmation notification(maybe with a different color or somekind of picture) Keep up the good work!