See https://commons.wikimedia.org/wiki/File:Navpop_illustration.png for the use of a really good tool, Navigation popups. They are interacting with the use of the toolserver, seemingly the XTools, which are taking a really long time to load when used in an article. One measurement of the api.php took 600,000 ms, or ten minutes to load.

Navpops fail to display during this time. However, navpops are available to the links displayed in watchlists (not in article space). Discussed in https://en.wikipedia.org/wiki/Wikipedia:Village_pump_%28technical%29#Navigation_popups_versus_alt_text \
which contains the 10-minute data point from a Firefox developer console, for the load of api.php in XTools