It'd be nice if the 'New Bookmark' dialog had an option to create a new
topic to put a bookmark in. Sometimes I'll want to bookmark a site that
doesn't belong in the topics I already have and I usually end up cancelling
the dialog, creating the topic, and then bookmarking the page. (Although I
guess I could bookmark it uncategorised and then create the topic and move
the bookmark there afterwards.) Having the option to add a new topic right
in the 'New Bookmark' dialog seems most intuitive. I wouldn't have to go
back or change anything while adding a bookmark that doesn't fit my current
list of topics.

I thought maybe it could be a right-click option within the list of topics,
but it looks like right-clicking right now just does the same thing as
left-clicking instead of providing additional options. Maybe this should be
changed so that I could rename, delete, and add topics (and "Show in
Bookmarks Bar"?) by right-clicking in that list? In other words,
right-clicking a topic in the New Bookmark dialog should do the same thing
as right-clicking on one in the Bookmarks editor with the additional option
of being able to create a new topic.