Bring Brow to Alfred
While Alfred will not recognize Brow's synced bookmarks on its own, it is terribly easy to teach Alfred that behaviour, and you don't need to have the Alfred Powerpack in order for this to work.
First, open the Alfred preferences and navigate to the Features tab and then to the Default Results section. There, click on the Advanced button:
Then, open a Finder window and navigate to the folder ~/Brow, where you should see folders named Firefox and Chrome (depending on your Brow settings). Inside these folders will be bookmark files created by Brow. Now choose one of these files, it doesn't matter which, drag it to Alfreds modal dialog table and drop it there:
Now Alfred has learned to work with Brow's bookmarks and the window should look like this:
Close the preferences window and you are ready. You can now use your Firefox and Chrome bookmarks in Alfred just like you can do with your Safari bookmarks.