I suggest using Chrome to develop with. It has very powerful development tools. There is a small bit of setup to maximize the development experience.

First, open the Chrome Dev Tools.

Then, scroll up in the Console to see that custom formatters failed to load.

Click on Settings (gear icon) in the top right.

Under Console, check "Enable custom formatters".

Reload the tab.

Custom formatters allow you to print ClojureScript data structures directly to the console.

If for any reason, the formatters seem to be not working, reload the tab again.