Firefox hangs while moving already downloaded part of the file to selected destination if it was just mounted on selection.

Steps to reproduce:
0. Set
  browser.download.useDownloadDir = false
  browser.download.lastDir = /media/unmounted/partition
1. Unmount the partition.
2. Start downloading a big file (several GiBs) from a server that gives several MiBs per second.
3. Mount the partition in the file selection dialog and select a directory on it as destination.

Then firefox freezes completely for some time. AFAIU it starts downloading somewhere ( /tmp ?) and then moves already downloaded part of the file to a new destination.

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: firefox 17.0.1+build1-0ubuntu0.12.04.1
ProcVersionSignature: Ubuntu 3.2.0-34.53-generic-pae 3.2.33
Uname: Linux 3.2.0-34-generic-pae i686
NonfreeKernelModules: nvidia
AddonCompatCheckDisabled: False
AlsaVersion: Advanced Linux Sound Architecture Driver Version 1.0.24.
ApportVersion: 2.0.1-0ubuntu15
Architecture: i386
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC1: i 2786 F.... pulseaudio
 /dev/snd/controlC0: i 2786 F.... pulseaudio
BuildID: 20121129162756
CRDA: Error: command ['iw', 'reg', 'get'] failed with exit code 1: nl80211 not found.
Card0.Amixer.info:
 Card hw:0 'PCH'/'HDA Intel PCH at 0xfa200000 irq 52'
   Mixer name : 'Realtek ALC892'
   Components : 'HDA:10ec0892,14627681,00100302'
   Controls : 44
   Simple ctrls : 21
Card1.Amixer.info:
 Card hw:1 'NVidia'/'HDA NVidia at 0xfa080000 irq 17'
   Mixer name : 'Nvidia GPU 16 HDMI/DP'
   Components : 'HDA:10de0016,10de0101,00100100'
   Controls : 24
   Simple ctrls : 4
Channel: Unavailable
Date: Mon Dec 17 23:38:26 2012
DefaultProfilePrefSources:
 prefs.js
 [Profile]/extensions/{b9db16a4-6edc-47ec-a1f4-b86292ed211d}/defaults/preferences/prefs-dwhelper.js
ForcedLayersAccel: False
IfupdownConfig:
 auto lo
 iface lo inet loopback
 #auto lo
IpRoute:
 default via 192.168.0.1 dev eth0 proto static
 10.0.3.0/24 dev lxcbr0 proto kernel scope link src 10.0.3.1
 169.254.0.0/16 dev eth0 scope link metric 1000
 192.168.0.0/24 dev eth0 proto kernel scope link src 192.168.0.104 metric 1
IwConfig:
 lo no wireless extensions.

 eth0 no wireless extensions.

 lxcbr0 no wireless extensions.
MarkForUpload: True
MostRecentCrashID: bp-b712e3bd-0b34-445d-80e3-685b62121215
Profile1Extensions: extensions.sqlite corrupt or missing
Profile1IncompatibleExtensions: Unavailable (corrupt or non-existant compatibility.ini or extensions.sqlite)
Profile1Locales: extensions.sqlite corrupt or missing
Profile1Plugins:
 Shockwave Flash - /usr/lib/adobe-flashplugin/libflashplayer.so (adobe-flashplugin)
 QuickTime Plug-in 7.6.6 - /usr/lib/mozilla/plugins/libtotem-narrowspace-plugin.so (totem-mozilla)
 DivX® Web Player - /usr/lib/mozilla/plugins/libtotem-mully-plugin.so (totem-mozilla)
 Windows Media Player Plug-in 10 (compatible; Totem) - /usr/lib/mozilla/plugins/libtotem-gmp-plugin.so (totem-mozilla)
 VLC Multimedia Plugin (compatible Totem 2.32.0) - /usr/lib/mozilla/plugins/libtotem-cone-plugin.so (totem-mozilla)
Profile1PrefSources: prefs.js
Profile1Themes: extensions.sqlite corrupt or missing
Profiles:
 Profile0 (Default) - LastVersion=17.0.1/20121129162756
 Profile1 - LastVersion=8.0/20111115184056 (Out of date)
RfKill:

RunningIncompatibleAddons: False
SourcePackage: firefox
SubmittedCrashIDs:
 bp-b712e3bd-0b34-445d-80e3-685b62121215
 bp-ef838a78-7d08-47b2-8d40-cca242121117
 bp-2a30c0ae-6941-44a7-bde1-deffe2111012
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 03/02/2011
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: V1.9
dmi.board.asset.tag: To be filled by O.E.M.
dmi.board.name: P67A-GD53 (MS-7681)
dmi.board.vendor: MSI
dmi.board.version: 1.0/2.0
dmi.chassis.asset.tag: To Be Filled By O.E.M.
dmi.chassis.type: 3
dmi.chassis.vendor: MSI
dmi.chassis.version: 1.0/2.0
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvrV1.9:bd03/02/2011:svnMSI:pnMS-7681:pvr1.0/2.0:rvnMSI:rnP67A-GD53(MS-7681):rvr1.0/2.0:cvnMSI:ct3:cvr1.0/2.0:
dmi.product.name: MS-7681
dmi.product.version: 1.0/2.0
dmi.sys.vendor: MSI