Narrowed browser tabs show the unread count for the entire user, rather than the unread count for messages in the current narrow. That's not particularly helpful for users who have multiple tabs for individual streams or topics. On the other hand, users who use a single tab to switch between narrows may still want to see their global unread count. Consider adding a user setting for how to compute the unread count in narrowed views.

Suggested by @meereeum.