Before we dive into the guts of the issue, we're going to need you to do
a few things for us, things that sometimes fix issues for users before
more extensive troubleshooting is needed. Can you please follow Steps 1-3
of our Solving Technical Issues checklist (confirm you're using the latest stable version of Firefox or Chrome and try witching browsers temporarily; turn off all extensions/addons/anti-virus; clear your cache) to see if
one of those components is causing the problem? We can only help if we
can recreate your issue, so it is important that you follow each step. If doing that fixes the issue, just let us know. Otherwise, move on to Step 4 , and we'll need all that information to further assist you. As a workaround in the meantime, once you've selected the zoom tool you should be able to arrow up/arrow down to select a zoom level within the menu, and you can also use the slider-control in the upper right corner or the map.