To be honest, i rarely search for caches using their gc-code. Rather by using keywords, e.g. parts of the name or by owner. And if you don't want to install the plugin, then try the following: go to the url coord.info/GCXXXXX and then look at the map in the listing. Then open a second tab in your favorite browser and go to the PGC live map and search the region.
Iti s not a convenient way, but you would not need to install the plugin, although it is great to have it in your browser ;-)