Previously in Firefox for Android, following a link to a PDF would prompt to download the PDF. It now opens the PDF in an internal PDF viewer, without saving it to the device.
For some sites, it seems possible to download (by using the "open in app" button, then downloading via the device's PDF viewer), but for some sites this does not seem possible, since there is no "open in app" button.
A solution to this would be to add a setting which restores the previous behaviour of downloading the PDF, since downloading PDFs is an essential feature of a browser.