How do I pin the menu?

I may be mistaken, but I am sure that in HT1/HT2 that I have had the left-hand menu pinned open for rapid browsing of the content.

I can’t seem to get this to work now - has it been broken?

In any case - being able to pin open the menu is really handy - there’s plenty of space to have it there all the time, and it would really speed things up when I am looking for a passage that I remember reading before.

Can it be done?