Zotero is a "personal research assistant" that can help you "help you collect, organize, cite, and share research".
It used to be available in Debian up to "stretch" but was removed from Debian "buster" after the Firefox 60 upgrade which broke the extension (864827). While work is underway to package the new 5.x version (871502), there are other alternatives to run Zotero in newer Debian releases.
flatpak remote-add --if-not-exists flathub https://flathub.org/repo/flathub.flatpakrepo flatpak install flathub org.zotero.Zotero
Then Zotero can be ran with:
flatpak run org.zotero.Zotero
Or by adding /var/lib/flatpak/exports/bin to your PATH:
echo 'export PATH=$PATH:/var/lib/flatpak/exports/bin' >> ~/.bashrc
In my experience (TheAnarcat), the "flatpak" Zotero was able to read the previous database directly without problems, but you might have to do some tweaks in the flatpak config if it's in a non-standard location. This is explained in the flathub page.
See also the FlatpakHowto.
There is also a Snap package but it does not seem up to date.
You can also download the official release and install it by hand.