A few months ago I complained about Firefox not being able to open PDFs without downloading them. Recently, I also wanted to start developing a custom Firefox addon to fix this behavior.

So what happened? I noticed that it didn’t happen on my work computer. Very strange…

I dug into the settings and found that on my work computer, Firefox was configured to open PDFs in Firefox, while on my home computer, it was configured to ask where to open them first. Changing it to “Open in Firefox” seems to work without downloading the PDF and saving it to the Downloads folder first. This was definitely not the case last year.

Searching online, I also found another hidden preference browser.download.open_pdf_attachments_inline. I guess it’s for when the HTTP response header Content-Disposition contains attachment. So if you enable it, it should also open those PDFs that are configured to be downloaded without downloading them.

Maybe the behavior changed when Firefox added the feature to open PDFs in the browser without downloading on Android?

At least I’m happy again. 😄