Use firefox-esr

Since Firefox 86, firefox freezes after some time when playing a video.
This only happens on wayland, but using xwayland causes weird stutters.
Downgrading is only meant to be a temporary solution.

users/simon/modules/programs.nix

@@ -136,7 +136,7 @@ in
   ] ++ lib.optionals nixosConfig.sbruder.gui.enable [
     # communication
     claws-mail # email client that looks ugly but just works
-    firefox-wayland # the least bad browser
+    firefox-esr # the least bad browser
     ((mumble.override { pulseSupport = true; }).overrideAttrs (o: o // {
       patches = o.patches ++ [
         # TODO: remove patch once stable release supports this