I think this one of those things that makes SuperMemo overly hard to use. You call it a Browser, but don't use the word "Browser" anywhere on the menus. When you open the "Browser", even the blue title bar at the top doesn't call it a "Browser". So it takes an "ah-ha" moment when the poor user (like me, who has been using SuperMemo for 5 years), finally learns the terminology.
Perhaps it should be called a "Viewer" or the menus should be called "Browse" instead of "View". I doubt you will change that because so many people are used to it, but the documentation can certainly explain the inconsistencies for those who actually do take the time to read the doc.
The page might still suggest (although not explicitly) that to open the Browser you would like for "Browser" somewhere on the "View" menu.