Sometimes you want to see hidden categories of the article you're reading just for a moment. You don't want to navigate away to the preferences to change the hidden category setting then navigate back to the page you were reading.
This especially happens for people that mostly just read but sometimes edit.
Since the hidden categories are there just hidden by CSS it would be trivial to add a checkbox in JavaScript to toggle between display:none and display:block
Version: unspecified
Severity: enhancement