A QGIS 3 locator plugin for Geomapfish services
Go to Plugins -> Manage and Install Plugins, look for Geomapfish Locator and install the plugin.
Settings -> Options -> Locator and open the configuration dialog for Geomapfish Locator
Add a new service from the plugin menu entry (Plugins-> Geomapfish Locator Filters -> Add new service)
Validate and start searching in the locator bar at the bottom left of the application.
Each service will create its own locator filter. All the filters can be seen under the locator settings
(in Settings -> Options -> Locator) and can be configured from there, including the prefix configuration.
If you want to avoid typing the prefix of the filter (gmf), enable the filter by default.