My browsers now have features to isolate tabs into groups. I use this feature to separate browsing into areas. For example, if one was both involved in full-time work and side-projects, as well as using their computer for relaxation, they could have 3 categories (e.g. Work, Side-project, Fun).
Being in these different browsing, as long as they are used diligently by the user, environments would be a very useful classifier of different kinds of browsing activity.
I am using Firefox and I use this add-on to separate work from play.