Firefox flatpak causes duplicate and blurry icon

[Rob Cork]

Plank version: 0.11.4
Linux Distribution: Linux Mint 19.3 Tricia x86_64
Window Manager: Mutter
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When launching a flatpak instance of Firefox, the Firefox icon will appear on plank and then a second later, a second blurry Firefox icon will appear. After about 15 seconds, the first icon disappears leaving just the blurry icon (see attached video)

The same thing happens if I launch Firefox directly from Plank. When i run Plank with verbose and debug enabled, when launching Firefox from Plank i see the following error:

[CRITICAL 17:45:19.266494] plank_application_dock_item_handle_name_changed: assertion 'old_name != NULL' failed

This error only appears when running in verbose mode. Debug mode alone does not show this error.

Here is the debug output:
[INFO 17:19:06.577431] [AbstractMain:229] Plank version: 0.11.4
[INFO 17:19:06.577496] [AbstractMain:230] Kernel version: 5.6.15-050615-generic
[INFO 17:19:06.577536] [AbstractMain:231] GLib version: 2.56.4 (2.54.1)
[INFO 17:19:06.577564] [AbstractMain:234] GTK+ version: 3.22.30 (3.22.26)
[INFO 17:19:06.577588] [AbstractMain:237] Wnck version: 3.24.1
[INFO 17:19:06.577622] [AbstractMain:238] Cairo version: 1.15.10
[INFO 17:19:06.577645] [AbstractMain:239] Pango version: 1.40.14
[INFO 17:19:06.577668] [AbstractMain:241] + Cairo/Gtk+ HiDPI support enabled
[INFO 17:19:06.577691] [AbstractMain:244] + Dynamic Quicklists support enabled
[INFO 17:19:06.577716] [AbstractMain:247] + XInput Barriers support enabled
[WARN 17:19:06.577749] [Environment:161] XDG_SESSION_CLASS not set in this environment!
[INFO 17:19:06.587734] [WindowControl:68] Window-manager: Mutter (Muffin)
[DEBUG 17:19:06.588248] [DockletManager:204] Loading module '/usr/lib/x86_64-linux-gnu/plank/docklets/libdocklet-clippy.so'
[INFO 17:19:06.588283] [DockletManager:107] Docklet 'clippy' registered
[DEBUG 17:19:06.588616] [DockletManager:204] Loading module '/usr/lib/x86_64-linux-gnu/plank/docklets/libdocklet-clock.so'
[INFO 17:19:06.588645] [DockletManager:107] Docklet 'clock' registered
[DEBUG 17:19:06.588900] [DockletManager:204] Loading module '/usr/lib/x86_64-linux-gnu/plank/docklets/libdocklet-cpumonitor.so'
[INFO 17:19:06.588927] [DockletManager:107] Docklet 'cpumonitor' registered
[DEBUG 17:19:06.589168] [DockletManager:204] Loading module '/usr/lib/x86_64-linux-gnu/plank/docklets/libdocklet-desktop.so'
[INFO 17:19:06.589194] [DockletManager:107] Docklet 'desktop' registered
[DEBUG 17:19:06.589469] [DockletManager:204] Loading module '/usr/lib/x86_64-linux-gnu/plank/docklets/libdocklet-trash.so'
[INFO 17:19:06.589498] [DockletManager:107] Docklet 'trash' registered
[INFO 17:19:06.589882] [AbstractMain:301] Running with 1 docks ('dock1')
[DEBUG 17:19:06.589918] [DockController:79] Create dock 'dock1' (config_folder = /home/rob/.config/plank/dock1)
[DEBUG 17:19:06.589998] [Settings:53] Bind 'PlankDockPreferences' to '/net/launchpad/plank/docks/dock1/'
[DEBUG 17:19:06.620009] [Preferences:349] Loading preferences from file '/home/rob/.local/share/plank/themes/iXi inDark/dock.theme'
[DEBUG 17:19:06.621622] [ItemFactory:176] Loading dock elements from '/home/rob/.config/plank/dock1/launchers'
[DEBUG 17:19:06.622150] [Preferences:349] Loading preferences from file '/home/rob/.config/plank/dock1/launchers/org.remmina.Remmina.dockitem'
[DEBUG 17:19:06.622902] [Preferences:349] Loading preferences from file '/home/rob/.config/plank/dock1/launchers/org.mozilla.firefox.dockitem'
[DEBUG 17:19:06.623394] [Preferences:349] Loading preferences from file '/home/rob/.config/plank/dock1/launchers/thunderbird.dockitem'
[DEBUG 17:19:06.623801] [Preferences:349] Loading preferences from file '/home/rob/.config/plank/dock1/launchers/org.gnome.Terminal.dockitem'
[DEBUG 17:19:06.624369] [Preferences:349] Loading preferences from file '/home/rob/.config/plank/dock1/launchers/trash.dockitem'
[DEBUG 17:19:06.629713] [Preferences:349] Loading preferences from file '/home/rob/.config/plank/dock1/launchers/telegramdesktop.dockitem'
[DEBUG 17:19:06.630340] [Preferences:349] Loading preferences from file '/home/rob/.config/plank/dock1/launchers/Restart Conky.dockitem'
[DEBUG 17:19:06.630914] [Preferences:349] Loading preferences from file '/home/rob/.config/plank/dock1/launchers/org.gnome.Evolution.dockitem'
[DEBUG 17:19:06.631959] [Preferences:349] Loading preferences from file '/home/rob/.config/plank/dock1/launchers/nemo.dockitem'
[DEBUG 17:19:06.632658] [Preferences:349] Loading preferences from file '/home/rob/.config/plank/dock1/launchers/beersmith3.dockitem'
[DEBUG 17:19:06.633134] [Preferences:349] Loading preferences from file '/home/rob/.config/plank/dock1/launchers/htop.dockitem'
[DEBUG 17:19:06.633637] [Preferences:349] Loading preferences from file '/home/rob/.config/plank/dock1/launchers/appimagekit-plexmediaplayer.dockitem'
[DEBUG 17:19:06.634118] [Preferences:349] Loading preferences from file '/home/rob/.config/plank/dock1/launchers/code.dockitem'
[DEBUG 17:19:06.634635] [Preferences:349] Loading preferences from file '/home/rob/.config/plank/dock1/launchers/sublime_text.dockitem'
[DEBUG 17:19:06.635133] [Preferences:349] Loading preferences from file '/home/rob/.config/plank/dock1/launchers/slack.dockitem'
[DEBUG 17:19:06.664046] [Unity:164] Initializing LauncherEntry support
[INFO 17:19:06.664349] [HideManager:618] Barriers enabled (XInput 2.3 support)
[DEBUG 17:19:06.664412] [PositionManager:677] Without draw_values there is trouble ahead
[DEBUG 17:19:06.666827] [Unity:133] com.canonical.Unity acquired
[INFO 17:19:06.780759] [DockRenderer:491] Cairo.SurfaceType: XLIB
[WARN 17:19:09.973190] Creating surface took WAY TOO LONG (40ms), enabled downscaling for this cache!

Output from neofetch if useful:
MMMMMMMMMMMMMMMMMMMMMMMMMmds+. rob@XPS-13-9300
MMm----::-://////////////oymNMd+` ---------------
MMd /++ -sNMd: OS: Linux Mint 19.3 Tricia x86_64
MMNso/` dMM `.::-. .-::.` .hMN: Host: XPS 13 9300
ddddMMh dMM :hNMNMNhNMNMNh: `NMm Kernel: 5.6.15-050615-generic
    NMm dMM .NMN/-+MMM+-/NMN` dMM Uptime: 28 mins
    NMm dMM -MMm `MMM dMM. dMM Packages: 2342
    NMm dMM -MMm `MMM dMM. dMM Shell: bash 4.4.20
    NMm dMM .mmd `mmm yMM. dMM Resolution: 1920x1200
    NMm dMM` ..` ... ydm. dMM DE: Cinnamon 4.4.8
    hMM- +MMd/-------...-:sdds dMM WM: Mutter (Muffin)
    -NMm- :hNMNNNmdddddddddy/` dMM WM Theme: Mint-Y-Dark-Blue (Mint-Y)
     -dMNs-``-::::-------.`` dMM Theme: Mint-Y-Blue [GTK2/3]
      `/dMNmy+/:-------------:/yMMM Icons: EPapirus [GTK2/3]
         ./ydNMMMMMMMMMMMMMMMMMMMMM Terminal: gnome-terminal
            .MMMMMMMMMMMMMMMMMMM CPU: Intel i7-1065G7 (8) @ 3.900GHz
                                      GPU: Intel Iris(R) Plus Graphics
                                      Memory: 2006MiB / 15594MiB