javascript blocked, map not showing

after installing the plugin no map is showing on the edit screen, no search etc.
there is a warning in the browser (chrome) console:

[blocked] The page at [mysite] ran insecure content from http://maps.google.com/maps/api/js?libraries=places&sensor=false&callback=simple_fields_googlemap.map_script_loaded.

similar message in firefox. why does the browser permit this javascript call?

http://wordpress.org/plugins/simple-fields-map-extension/