This adds an option to specify JSON you want to merge into the web application manifest. This allows you to edit existing properties as well as add new properties (what you specify to merge into the manifest file takes precedent over what XenForo generates by default). Note: the option is an "advanced" option, so you need to show advanced options to see it.
As an example, say you had an older version of XenForo (<2.2.13) where the
display
property wasn't set to
standalone, you could set
display
to
standalone and you could also add a screenshots property: