This feature already exists in Firefox Focus for Android, if anyone wants a first hand experience.
Platform request : Android
Unlike current behaviour on chromium based browsers where if you click on a PDF file Download link ( for example : https://international-school.cjd.de/de/file/51305/download ) or links that end with .pdf, direct download occures.
In firefox focus, when you click on a .pdf download link, a new tab open which allows the user to view/scroll/zoom the requested pdf file, and a download button appears on top of screen (just below the url bar), so user ensures that the right pdf is being downloaded, unlike chromium browser that directly starts the download.
Screenshot attached below of Firefox Focus behavior where if you click the above shared pdf link, rather than directly downloading the file immediatly itself. Firefox Focus opens the pdf in a new tab, lets you view/scroll/zoom/search the pdf, and then gives you an option to download on top left of screen to save the file to local device.
Any inputs/suggestions welcomed.