The 'Browse by category' box you see on the top of the page is known as the category quick filter. This filter allows reviewers to quickly view applications from a selected category and is available on all reviewing modes, including galleries.
By default, the 'Browse by category' option is visible to reviewers, however, you may wish to hide the category quick filter (particularly if you don't have many categories).
To hide the filter:
- Go to Settings > Reviewing > Score sets
- Click on the name of the score set you where you want to hind the category quick filter
- Go to the 'Display' tab
- Under 'Application list', untick Category quick filter
- Click Save