Firefox doesn't show the application dropbox for deb packages

[Juan Simón]

I have defined deb packages (in Gnome) to open with gdebi-gtk or file-roller (see screenshot 1).
I have defined the same in Firefox (see screenshot 2).
But when I download a deb package from web the Firefox download windows shows only a "Examine" button (see screenshot 3).

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: firefox 15.0.1+build1-0ubuntu0.12.04.1
ProcVersionSignature: Ubuntu 3.5.0-15.20-i7 3.5.4
Uname: Linux 3.5.0-15-i7 x86_64
NonfreeKernelModules: nvidia
AddonCompatCheckDisabled: False
AlsaVersion: Advanced Linux Sound Architecture Driver Version 1.0.25.
ApportVersion: 2.0.1-0ubuntu13
Architecture: amd64
AudioDevicesInUse:
 USUARIO ORDEN DE ACCESO PID
 /dev/snd/controlC1: simon 4624 F.... pulseaudio
 /dev/snd/controlC0: simon 4624 F.... pulseaudio
 /dev/snd/pcmC0D0p: simon 4624 F...m pulseaudio
BrokenPermissions:
 chrome/brief-custom-style.css (0411)
 <email address hidden> (0400)
 extensions/{D46E8522-6E86-44b1-A622-58C0668AD78E}.xpi (0400)
BuildID: 20120907231657
CRDA: Error: [Errno 2] No existe el archivo o el directorio
Card0.Amixer.info:
 Card hw:0 'Intel'/'HDA Intel at 0xfbff4000 irq 57'
   Mixer name : 'Realtek ALC889'
   Components : 'HDA:10ec0889,1458a022,00100004'
   Controls : 51
   Simple ctrls : 22
Card1.Amixer.info:
 Card hw:1 'NVidia'/'HDA NVidia at 0xfaffc000 irq 16'
   Mixer name : 'Nvidia GPU 0a HDMI/DP'
   Components : 'HDA:10de000a,10de0101,00100100'
   Controls : 24
   Simple ctrls : 4
Channel: Unavailable
Date: Tue Sep 18 13:13:28 2012
ForcedLayersAccel: False
IncompatibleExtensions: LastPass - <email address hidden>
IpRoute:
 default via 192.168.1.1 dev eth1 metric 100
 169.254.0.0/16 dev eth1 scope link metric 1000
 192.168.1.0/24 dev eth1 proto kernel scope link src 192.168.1.2
 192.168.2.0/24 dev eth0 proto kernel scope link src 192.168.2.1
IwConfig:
 eth0 no wireless extensions.

 eth1 no wireless extensions.

 lo no wireless extensions.
MostRecentCrashID: bp-1572d94b-afa0-4d99-8ca4-d1ee82120727
PrefSources:
 prefs.js
 [Profile]/<email address hidden>/defaults/preferences/defaults.js
 [Profile]/<email address hidden>/defaults/preferences/defaults.js
 [Profile]/<email address hidden>/defaults/preferences/prefs.js
Profiles: Profile0 (Default) - LastVersion=15.0.1/20120907231657 (In use)
RelatedPackageVersions:
 adobe-flashplugin 11.2.202.238-0precise1
 totem-mozilla 3.4.3-0ubuntu1~precise1
 gnome-shell 3.4.1-0ubuntu2
 mozplugger 1.14.3-7
RfKill: Can't open RFKILL control device: No such file or directory
RunningIncompatibleAddons: True
SourcePackage: firefox
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 02/01/2011
dmi.bios.vendor: Award Software International, Inc.
dmi.bios.version: FD
dmi.board.name: X58A-UD5
dmi.board.vendor: Gigabyte Technology Co., Ltd.
dmi.chassis.type: 3
dmi.chassis.vendor: Gigabyte Technology Co., Ltd.
dmi.modalias: dmi:bvnAwardSoftwareInternational,Inc.:bvrFD:bd02/01/2011:svnGigabyteTechnologyCo.,Ltd.:pnX58A-UD5:pvr:rvnGigabyteTechnologyCo.,Ltd.:rnX58A-UD5:rvr:cvnGigabyteTechnologyCo.,Ltd.:ct3:cvr:
dmi.product.name: X58A-UD5
dmi.sys.vendor: Gigabyte Technology Co., Ltd.

[Chris Coulson (chrisccoulson)]

Thanks, but as explained in the bug reporting guidelines (https://wiki.ubuntu.com/MozillaTeam/Bugs), it's not really necessary to report this bug any more times

[Juan Simón (simonbcn)]

I think this isn't a duplicate.
It works well in another mimetypes, for example PDF (see screenshot).
Why doesn't work with DEB packages?
How can I reset the DEB associations in Firefox?

[Juan Simón (simonbcn)]

Where does Firefox get the mimetypes associations?

[Chris Coulson (chrisccoulson)]

Yes, I can assure you that it's a duplicate. There are various symptoms that are all caused by the same bug

[Juan Simón (simonbcn)]

ok, where does Firefox get the mimetypes associations?

[Adolfo Jayme Barrientos (fitojb)]

I think it uses shared-mime-info.