thunderbird main window can't be started from unity starter icon if email compose window is opened

[Karl-Philipp Richter]

If the email compose window has been opened in the `thunderbird` main window and then the main window is closed so that the compose window stays open there's no way to open the main window again without closing the compose window.

ProblemType: Bug
DistroRelease: Ubuntu 15.04
Package: thunderbird 1:38.3.0+build1-0ubuntu0.15.04.1
Uname: Linux 4.2.2-040202-generic x86_64
AddonCompatCheckDisabled: False
ApportVersion: 2.17.2-0ubuntu1.5
Architecture: amd64
AudioDevicesInUse:
 BEN. PID ZUGR. BEFEHL
 /dev/snd/controlC0: richter 3036 F.... pulseaudio
BootDmesg: (Nothing has been logged yet.)
BuildID: 20150930121410
Channel: Unavailable
Date: Mon Oct 19 17:18:53 2015
Extensions: extensions.sqlite corrupt or missing
ForcedLayersAccel: False
IfupdownConfig:
 # interfaces(5) file used by ifup(8) and ifdown(8)
 auto lo
 iface lo inet loopback
IncompatibleExtensions: Unavailable (corrupt or non-existant compatibility.ini or extensions.sqlite)
InstallationDate: Installed on 2015-09-14 (34 days ago)
InstallationMedia: Ubuntu 15.04 "Vivid Vervet" - Release amd64 (20150422)
IpRoute:
 default via 192.168.179.1 dev eth2 proto static metric 100
 10.0.3.0/24 dev lxcbr0 proto kernel scope link src 10.0.3.1
 169.254.0.0/16 dev eth2 scope link metric 1000
 192.168.122.0/24 dev virbr0 proto kernel scope link src 192.168.122.1
 192.168.179.0/24 dev eth2 proto kernel scope link metric 100
Locales: extensions.sqlite corrupt or missing
MarkForUpload: True
Plugins:
 IcedTea-Web Plugin (using IcedTea-Web 1.5.2 (1.5.2-1ubuntu2)) - /usr/lib/jvm/java-7-openjdk-amd64/jre/lib/amd64/IcedTeaPlugin.so (icedtea-7-plugin)
 iTunes Application Detector - /usr/lib/mozilla/plugins/librhythmbox-itms-detection-plugin.so (rhythmbox-mozilla)
 Shockwave Flash - /usr/lib/flashplugin-installer/libflashplayer.so
PrefSources:
 prefs.js
 [Profile]/extensions/{847b3a00-7ab1-11d4-8f02-006008948af5}/defaults/preferences/enigmail.js
 [Profile]/extensions/{e2fda1a4-762b-4020-b5ad-a41df1933103}/defaults/preferences/lightning.js
Profiles: Profile0 (Default) - LastVersion=38.3.0/20150930121410 (In use)
RelatedPackageVersions:
 icedtea-7-plugin 1.5.2-1ubuntu2
 rhythmbox-mozilla 3.1-1ubuntu3
RunningIncompatibleAddons: False
SourcePackage: thunderbird
SystemImageInfo:
 current build number: 0
 device name:
 channel: daily
 last update: Unknown
Themes: extensions.sqlite corrupt or missing
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 07/12/2013
dmi.bios.vendor: LENOVO
dmi.bios.version: 71CN51WW(V1.21)
dmi.board.asset.tag: No Asset Tag
dmi.board.name: INVALID
dmi.board.vendor: LENOVO
dmi.board.version: 31900003WIN8 STD MLT
dmi.chassis.asset.tag: No Asset Tag
dmi.chassis.type: 10
dmi.chassis.vendor: LENOVO
dmi.chassis.version: Lenovo IdeaPad Z500 Touch
dmi.modalias: dmi:bvnLENOVO:bvr71CN51WW(V1.21):bd07/12/2013:svnLENOVO:pn20221:pvrLenovoIdeaPadZ500Touch:rvnLENOVO:rnINVALID:rvr31900003WIN8STDMLT:cvnLENOVO:ct10:cvrLenovoIdeaPadZ500Touch:
dmi.product.name: 20221
dmi.product.version: Lenovo IdeaPad Z500 Touch
dmi.sys.vendor: LENOVO

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Bob Briscoe (m-bob-q)]

Solution: With the focus on the open compose window, select from menu: Tools > Mail & Newsgroups [Ctrl+1]

There are related inconsistencies though.
* If an email is opened for reading in a new window, the shortcut key changes: Tools > Mail & Newsgroups [Alt+1]
* If only search, message filters, activity manager and preferences windows are open, no top level menus are visible and neither [Ctrl+1] nor [Alt+1] does anything.

The latter is a bug. However, there is a work-round that works in the other cases as well:
* Launcher > right click Thunderbird icon > "Compose New Message", which then gives access to the first solution above.

This problem is irritating for me, because I often have large numbers of Thunderbird windows open, and until I found the above solutions/workrounds, if I accidentally closed the main window (which I have done many times), in order to reopen it, I had to close all the other windows, thus losing track of all my work-in-progress when I restarted Thunderbird.