Due to a current lack of usable Weechat relay clients on Linux that work well with mobile display sizes, and a lack of free time on my part to write one, I've come up with this simple (albeit not elegant) way to "run" Glowing Bear in a way that doesn't take up valuable tab space in Firefox. This essentially just runs a new Firefox window in kiosk mode, so that the tab bar, menus, etc are hidden, and makes it "feel" a bit more like a "native app" than a web thing running in a browser tab.

~/.local/share/applications/weechat.desktop:

[Desktop Entry]
Name=Weechat
Exec=firefox --kiosk --new-window https://glowing-bear.org
Terminal=false
Type=Application
StartupNotify=true
X-Purism-FormFactor=Workstation;Mobile;

I did experiment with using webkit2gtk and having a very simple wrapper to load Glowing Bear, but the performance of webkit2gtk is not great... scrolling in Glowing Bear was very slow even on the Librem 5.