Does the job, thanks – tested with the PDF reports under https://ec.europa.eu/digital-single-market/en/news/annual-self-assessment-reports-signatories-code-practice-disinformation-2019#block-views-39e10d54fad34071dca96fe7d7133f38

Four stars here.

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Five stars to Display inline https://addons.mozilla.org/addon/display-inline/ for having a longer history and offering a support address.

yes! gets the job done

some websites send certain files with an "attachment" header and firefox shows a popup-dialog to "open with X or save file", even for files that firefox could display, like *.htm or *.jpg or *.pdf or *.mp3

here is a test page:
http://test.greenbytes.de/tech/tc2231/#attwithasciifilename

that behavior is desired in some cases, with large files or with actual "download links", but mostly its annoying and we just want to see the file ....

.... and find this addon to silently "rewrite" the disposition header. no more popup, just shut up and show me your bits!

via
https://stackoverflow.com/questions/3251575/how-to-ignore-content-disposition-attachment-in-firefox

Your plugin works maybe half the time. For example, this link doesn't work: (https://www.st.com/resource/en/datasheet/stusb4500.pdf). I tried this link with the "Always Preview" plugin and it worked fine.

doesn't work for https://github.com/progit/progit2/releases/download/2.1.109/progit.pdf

Solved the problem with .torrent files not opening automatically with torrent-client.

Linux Mint, Firefox Quantum 63.0 64bit

Works great in Firefox 63.0.3!

I only wish I could selectively enable/disable it via a toolbar button and/or a configurable whitelist and blacklist of host names. Workaround: go to about:addons and disable/enable the extension, this takes effect immediately.

Perfect solution to force Firefox to remember default action when opening a file

Works great however it would be great if it had a text field where I could enter the websites I don't want to be mangled by this add-on.

One site, one line.

Subdomains will have to be matched too, e.g.

domain.com should also match one.domain.com and two.domain.com

A "Save" button would be nice, so that Firefox wouldn't save the contents of this field on every key press.

https://support.mozilla.org/en-US/questions/1039640

Brought me here. Fixed my exact same issue with qBittorrent

I have a problem to download attachments on Gmail. When I click on individual download arrow nothing happens. Only works if I click on all files download arrow. Can you fix it? Thanks a lot!

It is working on firefox 57

Does not work for me at all.
EDIT to respond to author's reply: I think I debugged it! In my particular case the server sends a weird header:

Content-Disposition: inline; filename=example.jpg

Firefox interprets it as attachment disposition. Your extension should probably handle this case too.

Holy crap, an inline disposition plugin that works!

Thanks. The only one I found working on firefox 57

Thank You for porting to 57+