Comment 19 for bug 751374

OK, here's how to reproduce the bug from a default Ubuntu install:

(Note: When Ubuntu is installed by default, there is only one file browser, Nautilus. In the "Preferred Applications" utility (easily searched for in the Launcher), there is no place to specify one's favorite File Manager/File Browser. But a graphical utility to set this does exist, unbeknownst to most users, called "exo-preferred-applications". But there's no icon ever presented for this in the Launcher. You can run "exo-preferred-applications" from the command line.)

1) In a Terminal, run "exo-preferred-applications". Go to the "Utilities" tab, and note that the "File Manager" is set, by default, to "No application selected". In this state, the bug does not occur. Close "exo-preferred-applications" for now.

2) Install a second File Manager/File Browser, say, Thunar.

3) In Firefox, download some file, say a .pdf. Once downloaded, double-click the .pdf in the "Downloads" window to try to open it. Now there are two possible File Managers to pick from, so a dialog is presented for you to select your default File Manager (see screenshot). Choose Nautilus, and click OK. NOW THE BUG IS IN EFFECT! And you'll promptly be presented with the error message window ('Could not display "/home/myuser/Downloads/sample.pdf" The location is not a folder'), instead of the .pdf opening properly. And now you'll also be screwed in the way the original poster of this bug explained: no files can be launched from the "Files & Folders" utility either (in the Dash, or Launcher).

4) Open "exo-preferred-applications" again. Go to the "Utilities" tab, and note that the "File Manager" is now set to Nautilus. And you can't choose "No application selected" anymore, you can only select between Nautilus and Thunar. So you can't go back to the state before the bug occurred. But you can set Thunar to be the default File Manager, as a workaround.

Now, PhobosK, do you see the relevance of my previous post? It nailed down exactly where this error occurs, and explains why the workaround works.

Most Ubuntu users will never install a second File Manager, and therefore never run into this bug. But I had to install Thunar, as a workaround to another Nautilus bug: https://bugs.launchpad.net/ubuntu/+source/gvfs/+bug/574693

The solution to this issue might need to be twofold:

1) Allow the selecting of preferred File Manager in the "Preferred Applications" utility. And the default should be "Nautilus", not "No application selected".

2) Nautilus should successfully open URI's beginning with "file:///" and ending with a filename, just like Thunar can, as per my previous post.

And perhaps a better title for this bug (although I know it's way too long) might be 'Launcher/Dash can't directly open files, unless 'File Manager' is set to "No application selected" in "exo-preferred-applications"'