I am running Debian 10.6, XFCE desktop and the lightdm display manager. After a recent system upgrade I noticed that the mouse pointer "spins" for up to a minute after launching Firefox. I tried all the usual things like disabling plugins and extensions, etc etc, but nothing helped, although starting in sfafe mode did not exhibit the spinning mouse pointer. What I did find was that editing /usr/share/applications/firefox-esr.desktop and changing StartupNotify=true to StartupNotify=false eliminated the distraction.
I changed it about a week ago and have not seen any abnormal behavior. Does anybody know of any issues with changing that variable?