I have set basically all file types in Edit->Preferences->Applications to "Always ask" because I want to decide for every file whether I want to open or save it.

My usual workflow when saving a file to disk is opening the Firefox downloads list and double clicking the file from there after it has finished downloading. However, Firefox uses nonsensical applications to open the files when clicking them in the download list.

E.g. Firefox uses Krita (used for painting and illustration) to open PDF files. Even worse: when right clicking a file and selecting "Open containing folder" Firefox will open the folder using Filelight, KDE's disk space analyzer tool.

I am assuming that Firefox is using the applications that have the note "(default)" next to their name in the select list on Edit->Preferences->Applications. How does Firefox determine which application is the default? And how can I change this?

Note: I have already seen Application that would set default application for file types and How can I choose the default application for opening files in Firefox? and do not want to set Firefox to always open a file using a specific application. I want to leave the settings on Edit->Preferences->Applications at "Always ask" and only change the application that is used when actively clicking the file in the downloads list.

2 Answers 2


I was having the same problem on Ubuntu. Running the following commands in the terminal worked for me:

$ cd /usr/share/applications
$ xdg-mime default evince.desktop application/pdf

According to this answer, you may check $HOME/.local/share/applications as well, but that wasn't needed for me.

  • Welcome to StackExchange. You should include a tad more details in your answer, as it stands it does not fully answer the OP: it works, but why? Concise answers are favored, but not to the detriment of an explanation. Aug 1, 2016 at 5:54
  • @MariusMatutiae, thanks. If I'd known why, I'd have written an explanation. I had the same problem and found a solution elsewhere, so I thought I might as well share my solution. I'd also be very curious as to why this happens (the problem appeared for my when installing and uninstalling Adobe Reader).
    – Dan
    Aug 3, 2016 at 18:47

Firefox determines the application from the mime type info sent from the server in the header of the download file. The file extension does not matter.

But some servers just do not send this info. So far, I have not found a way to set the default behaviour for that case.

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