There may be other causes of firefox hanging. Though in my troubleshooting of this it was mentioned firefox can end up later updating to the snap version after you've installed the deb version, unless you take some steps to prevent that from happenin...
I am experiencing this too. firefox on a very recent insall of Kubuntu 25.04. 138.0.1 (64bit).This is the snap distribution of firefox. I'm using extensions darkreader, Enhancer for Youtube, uBlock origin, and youtube column customizer. But I don't t...
