Mission planner crashes when fetching beta-firmware list

Current beta, after clicking "beta firmware" , and OK on the stability warning:

HUD resize 5 5
Open MissionPlanner.GCSViews.InitialSetup HWConfig
INFO MissionPlanner.Utilities.adsb - adsb connect loop
Open MissionPlanner.GCSViews.ConfigurationView.ConfigFirmware Install Firmware
INFO MissionPlanner.Controls.ProgressReporterDialogue - RunBackgroundOperation
INFO MissionPlanner.Controls.ProgressReporterDialogue - Focus ctl
INFO MissionPlanner.Controls.ProgressReporterDialogue - in focus invoke
INFO MissionPlanner.Controls.ProgressReporterDialogue - DoWork
INFO MissionPlanner.Utilities.Firmware - getFWList
INFO MissionPlanner.Utilities.Firmware - url: https://raw.github.com/diydrones/binary/master/Firmware/firmware2.xml
INFO MissionPlanner.Utilities.Firmware - Get url http://firmware.diydrones.com/Plane/stable/apm2-hilsensors/git-version.txt
INFO MissionPlanner.Utilities.Firmware - Get url http://firmware.diydrones.com/Rover/stable/apm2/git-version.txt
INFO MissionPlanner.Utilities.Firmware - Get url http://firmware.diydrones.com/Plane/stable/apm2/git-version.txt
INFO MissionPlanner.Utilities.Firmware - Get url http://firmware.diydrones.com/Copter/stable/apm2-quad/git-version.txt
INFO MissionPlanner.Utilities.Firmware - Get url http://firmware.diydrones.com/Copter/stable/apm2-tri/git-version.txt
INFO MissionPlanner.Utilities.Firmware - Get url http://firmware.diydrones.com/Copter/stable/apm2-hexa/git-version.txt
INFO MissionPlanner.Utilities.Firmware - APMVERSION: ArduCopter V3.1.3
INFO MissionPlanner.Utilities.Firmware - Get url http://firmware.diydrones.com/Copter/stable/apm2-y6/git-version.txt
INFO MissionPlanner.Utilities.Firmware - APMVERSION: ArduCopter V3.1.3
INFO MissionPlanner.Utilities.Firmware - APMVERSION: ArduRover v2.45
INFO MissionPlanner.Utilities.Firmware - Get url http://firmware.diydrones.com/Copter/stable/apm2-octa-quad/git-version.txt
INFO MissionPlanner.Utilities.Firmware - Get url http://firmware.diydrones.com/Copter/stable/apm2-octa/git-version.txt
INFO MissionPlanner.Utilities.Firmware - APMVERSION: ArduCopter V3.1.3
INFO MissionPlanner.Utilities.Firmware - APMVERSION: ArduPlane V3.0.1
INFO MissionPlanner.Utilities.Firmware - Get url http://firmware.diydrones.com/Copter/stable/apm2-heli/git-version.txt
INFO MissionPlanner.Utilities.Firmware - Get url http://firmware.diydrones.com/Copter/stable/apm2-quad-hil/git-version.txt
INFO MissionPlanner.Utilities.Firmware - Get url http://firmware.diydrones.com/Copter/stable/apm2-heli-hil/git-version.txt
INFO MissionPlanner.Utilities.Firmware - APMVERSION: ArduCopter V3.1.3
INFO MissionPlanner.Utilities.Firmware - APMVERSION: ArduCopter V3.1.3
INFO MissionPlanner.Utilities.Firmware - APMVERSION: ArduPlane V3.0.1
INFO MissionPlanner.Utilities.Firmware - APMVERSION: ArduCopter V3.1.3
INFO MissionPlanner.Utilities.Firmware - APMVERSION: ArduCopter V3.1.3
INFO MissionPlanner.Utilities.Firmware - APMVERSION: ArduCopter V3.1.3
INFO MissionPlanner.Utilities.Firmware - APMVERSION: ArduCopter V3.1.3
INFO MissionPlanner.Utilities.Firmware - load done
INFO MissionPlanner.Controls.ProgressReporterDialogue - DoWork Done
INFO MissionPlanner.Utilities.adsb - adsb connect loop
CustomMessageBox thread calling Base Thread
CustomMessageBox thread running Base Thread
INFO MissionPlanner.Utilities.adsb - adsb connect loop
INFO MissionPlanner.Controls.ProgressReporterDialogue - RunBackgroundOperation
INFO MissionPlanner.Controls.ProgressReporterDialogue - Focus ctl
INFO MissionPlanner.Controls.ProgressReporterDialogue - in focus invoke
[xcb] Too much data requested from _XRead
[xcb] This is most likely caused by a broken X extension library
[xcb] Aborting, sorry about that.
mono: ../../src/xcb_io.c:736: _XRead: Assertion `!xcb_xlib_too_much_data_requested' failed.
Stacktrace:

at <0xffffffff>
at (wrapper managed-to-native) System.Windows.Forms.X11Keyboard.XCreateFontSet (intptr,string,intptr&,int&,intptr) <0xffffffff>
at System.Windows.Forms.X11Keyboard.CreateOverTheSpotXic (intptr,intptr) <0x000af>
at System.Windows.Forms.X11Keyboard.CreateXic (intptr,intptr) <0x000d7>
at System.Windows.Forms.X11Keyboard.CreateXicForWindow (intptr) <0x00037>
at System.Windows.Forms.X11Keyboard.FocusIn (intptr) <0x00087>
at System.Windows.Forms.XplatUIX11.SetFocus (intptr) <0x000b3>
at System.Windows.Forms.XplatUI.SetFocus (intptr) <0x0001f>
at System.Windows.Forms.Control.Select (System.Windows.Forms.Control) <0x00297>
at System.Windows.Forms.Control.FocusInternal (bool) <0x0006b>
at System.Windows.Forms.Form.FocusInternal (bool) <0x00047>
at System.Windows.Forms.Control.Focus () <0x00018>
at MissionPlanner.Controls.ProgressReporterDialogue.ProgressReporterDialogue_Load (object,System.EventArgs) <0x00013>
at System.Windows.Forms.Form.OnLoad (System.EventArgs) <0x00075>
at System.Windows.Forms.Form.OnLoadInternal (System.EventArgs) <0x0007f>
at System.Windows.Forms.Form.OnCreateControl () <0x00053>
at System.Windows.Forms.Control.CreateControl () <0x0011f>
at System.Windows.Forms.Control.WmShowWindow (System.Windows.Forms.Message&) <0x00167>
at System.Windows.Forms.Control.WndProc (System.Windows.Forms.Message&) <0x002d3>
at System.Windows.Forms.ScrollableControl.WndProc (System.Windows.Forms.Message&) <0x0001b>
at System.Windows.Forms.ContainerControl.WndProc (System.Windows.Forms.Message&) <0x0005b>
at System.Windows.Forms.Form.WndProc (System.Windows.Forms.Message&) <0x00253>
at System.Windows.Forms.Control/ControlWindowTarget.OnMessage (System.Windows.Forms.Message&) <0x00025>
at System.Windows.Forms.Control/ControlNativeWindow.WndProc (System.Windows.Forms.Message&) <0x00036>
at System.Windows.Forms.NativeWindow.WndProc (intptr,System.Windows.Forms.Msg,intptr,intptr) <0x00310>
at System.Windows.Forms.XplatUIX11.SendMessage (intptr,System.Windows.Forms.Msg,intptr,intptr) <0x003f3>
at System.Windows.Forms.XplatUIX11.MapWindow (System.Windows.Forms.Hwnd,System.Windows.Forms.WindowType) <0x001df>
at System.Windows.Forms.XplatUIX11.CreateWindow (System.Windows.Forms.CreateParams) <0x00bab>
at System.Windows.Forms.XplatUI.CreateWindow (System.Windows.Forms.CreateParams) <0x0001f>
at System.Windows.Forms.NativeWindow.CreateHandle (System.Windows.Forms.CreateParams) <0x0003f>
at System.Windows.Forms.Control.CreateHandle () <0x00069>
at System.Windows.Forms.Form.CreateHandle () <0x0002b>
at System.Windows.Forms.Control.CreateControl () <0x00087>
at System.Windows.Forms.Control.SetVisibleCore (bool) <0x00083>
at System.Windows.Forms.Form.SetVisibleCore (bool) <0x002ef>
at System.Windows.Forms.Control.set_Visible (bool) <0x00032>
at (wrapper remoting-invoke-with-check) System.Windows.Forms.Control.set_Visible (bool) <0xffffffff>
at System.Windows.Forms.Application.RunLoop (bool,System.Windows.Forms.ApplicationContext) <0x002ef>
at System.Windows.Forms.Form.ShowDialog (System.Windows.Forms.IWin32Window) <0x008a3>
at System.Windows.Forms.Form.ShowDialog () <0x00013>
at MissionPlanner.Controls.ProgressReporterDialogue.RunBackgroundOperationAsync () <0x000ef>
at (wrapper remoting-invoke-with-check) MissionPlanner.Controls.ProgressReporterDialogue.RunBackgroundOperationAsync () <0xffffffff>
at MissionPlanner.GCSViews.ConfigurationView.ConfigFirmware.UpdateFWList () <0x001f3>
at MissionPlanner.GCSViews.ConfigurationView.ConfigFirmware.lbl_devfw_Click (object,System.EventArgs) <0x0008b>
at System.Windows.Forms.Control.OnClick (System.EventArgs) <0x00069>
at System.Windows.Forms.Control.HandleClick (int,System.Windows.Forms.MouseEventArgs) <0x000b7>
at System.Windows.Forms.Control.WmLButtonUp (System.Windows.Forms.Message&) <0x000fd>
at System.Windows.Forms.Control.WndProc (System.Windows.Forms.Message&) <0x00213>
at System.Windows.Forms.Label.WndProc (System.Windows.Forms.Message&) <0x00033>
at System.Windows.Forms.Control/ControlWindowTarget.OnMessage (System.Windows.Forms.Message&) <0x00025>
at System.Windows.Forms.Control/ControlNativeWindow.WndProc (System.Windows.Forms.Message&) <0x00036>
at System.Windows.Forms.NativeWindow.WndProc (intptr,System.Windows.Forms.Msg,intptr,intptr) <0x00310>
at System.Windows.Forms.XplatUIX11.DispatchMessage (System.Windows.Forms.MSG&) <0x0001f>
at System.Windows.Forms.XplatUI.DispatchMessage (System.Windows.Forms.MSG&) <0x0001f>
at System.Windows.Forms.Application.RunLoop (bool,System.Windows.Forms.ApplicationContext) <0x00c7f>
at System.Windows.Forms.Application.Run (System.Windows.Forms.ApplicationContext) <0x0005f>
at System.Windows.Forms.Application.Run (System.Windows.Forms.Form) <0x00033>
at MissionPlanner.Program.Main (string[]) <0x00a5f>
at (wrapper runtime-invoke) .runtime_invoke_void_object (object,intptr,intptr,intptr) <0xffffffff>

Native stacktrace:

```
mono() [0x4b73d8]
/lib/x86_64-linux-gnu/libpthread.so.0(+0x10340) [0x7f729f667340]
/lib/x86_64-linux-gnu/libc.so.6(gsignal+0x39) [0x7f729f2c7f79]
/lib/x86_64-linux-gnu/libc.so.6(abort+0x148) [0x7f729f2cb388]
/lib/x86_64-linux-gnu/libc.so.6(+0x2fe36) [0x7f729f2c0e36]
/lib/x86_64-linux-gnu/libc.so.6(+0x2fee2) [0x7f729f2c0ee2]
/usr/lib/x86_64-linux-gnu/libX11.so.6(_XRead+0xd5) [0x7f72968d3925]
/usr/lib/x86_64-linux-gnu/libX11.so.6(_XRead32+0x24) [0x7f72968d43b4]
/usr/lib/x86_64-linux-gnu/libX11.so.6(XListFontsWithInfo+0x368) [0x7f72968b6fc8]
/usr/lib/x86_64-linux-gnu/libX11.so.6(+0x7358d) [0x7f729690a58d]
/usr/lib/x86_64-linux-gnu/libX11.so.6(XCreateOC+0xeb) [0x7f72968c2d4b]
/usr/lib/x86_64-linux-gnu/libX11.so.6(XCreateFontSet+0x5c) [0x7f72968b79cc]
[0x403a3f8b]
```

Debug info from gdb:

ptrace: Operation not permitted.
No threads.
#

Got a SIGABRT while executing native code. This usually indicates
a fatal error in the mono runtime or one of the native libraries
# used by your application.

Aborted (core dumped)

Start at MissionPlanner.GCSViews.ConfigurationView.ConfigFirmware.lbl_devfw_Click and UpdateFWList, then follow the ProgressReporterDialogue.ProgressReporterDialogue_Load stack frames. Reproduce the beta-firmware fetch under the reported Mono/X11 setup and determine whether the crash is triggered by Mission Planner or the native X11 path. Done means opening the beta-firmware list no longer aborts the application.

Written by the indexing model from the issue text.