Gnome Tracker: How to change the list of searched programs?

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Hi, I installed tracker-thunderbird-plugin and it seems to index my emails just fine. At least that is what the little status bar in Thunderbird is saying.

But when I use the search field in Gnome it does not return any results from my emails. So, I took a look at the Search options under Settings and found out that Thunderbird is not listed as one of the programs to be searched through.

How can I add Thunderbird to this list?

Side comment: Tracker on CLI:

tracker search nobody@fedoraproject.org

only returns something if I add ~/.thunderbird to the list of indexed folders.