MusicBrainz.org offers browser search plugins with a name pattern like "MusicBrainz: Artist". In Mozilla Firefox, these offerings are displayed in the browser's search field drop down menu. If one clicks for example the aforementioned plugin, it gets installed but with the string " (indexed)" appended at the end of its name.
Usually, when a search plugin is installed, it is then hidden from the list of offered plugins. I believe this is done by matching the names but since the names don't match, it results in useless bloating of the menu.
So, it's more of a cosmetic issue than a functionality one. And in the same vein, a suggested fix would be removing the " (indexed)" part from the search plugin XML files. At least I'm not aware of any added value it might have.
(This used to be easily fixed locally but Firefox has for some time now been using cached copies of search plugins instead of the source XML files, so I thought getting to the source of the problem might be worth the while.)