Comment 6 for bug 1035221

After a lot of digging into the various involved components including some "stracing" I found out why it didn't work and how to fix this:

It seems the default applications are found via .desktop files in /home/<user>/.local/share/applications. I had some older entries in there, probably from Ubuntu editions from a few years back (I am not a fan of re-installing and usually update from one to the next version). There were several firefox entries in there, when I removed all of them, I could not select firefox any more as default application in the system settings, however when I copied over the firefox.desktop entry from /usr/share/applications/ and re-selected firefox as the default application, I can now open http-links from all the applications again.

Not sure who or what is to blame here, somehow my deleted-files folder does not show the removed .desktop files any more, so I cannot post them to allow for closer analysis, maybe the original reporter with the same problem can post the files.