On base install of Kubuntu 19.04, Enpass is unable to authorize sync with Dropbox (via Firefox). An error appears when clicking "Authorize" on the Dropbox sync page. I believe this is because newer versions of Kubuntu omit the `desktop-file-utils` package. This can be fixed by running the following commands in terminal:
sudo apt install desktop-file-utils
sudo update-desktop-database
After this, run the sync setup again and it should work.