Bug 1770636 - Fix StartupWMClass of flatpak package to match actually-used...

Bug 1770636 - Fix StartupWMClass of flatpak package to match actually-used WMClass. r=jhorak, a=dmeehan

Pending further changes iff we want to do them (like comment 5), this is the
right thing to do.

I'm not a fan of comment 5 since in the past I've been bitten by Wayland
compositors not comparing stuff case-insensitively, so making everything
lowercase is probably simpler.

Differential Revision: https://phabricator.services.mozilla.com/D149911

taskcluster/docker/firefox-flatpak/org.mozilla.firefox.desktop

@@ -51,7 +51,7 @@ StartupNotify=true
 Categories=Network;WebBrowser;
 Keywords=web;browser;internet;
 Actions=new-window;new-private-window;profile-manager-window;
-StartupWMClass=Firefox
+StartupWMClass=firefox
 
 
 [Desktop Action new-window]