After buying a counter or wall, the item stays in your hand: every click on an empty tile buys and places another one, until you press Esc or right-click. It also stops if you run out of money.
Right-clicking the board no longer opens the browser's menu.
The hints under the board and in the shop say so.
The animated clip (114, recorded on v0.0.50) shows one Wall purchase placed four times by clicking, then a right-click to stop. The hint text has changed since (it now also mentions R and replacing counters), but the placing works the same.