Now, you have 2 options for proceeding from here. Both options work well. Pick one. Your choice.
2a. Click the MapPost browser extension button near the top of the Safari browser, in the tool bar and just to the left of the address bar.
2b. 'Right Click' ('Control Click' on a Mac) on the browser window to display an extension pop-up. Then click the 'Save to MapPost' option in the pop-up.