Error opening browser in VNC session: cannot open display: :1.0

### Setup My goal is to use a web browser in a VNC session. I followed this page to install tightvncserver with xfce4. The session works fine, i.e. I am able to open all other GUI programs. I ran apt install firefox and snap install brave. Connection is via SSH jump and then port forwarding between localhost of both client and server. ### Symptoms When I try to launch browsers from GUI, nothing happens. On the command line I get for Firefox:

Client is not authorized to connect to ServerError: cannot open display: :1.0

And for Brave:

Client is not authorized to connect to Server[11997:11997:0704/151224.702071:ERROR:ozone_platform_x11.cc(247)] Missing X server or $DISPLAY
[11997:11997:0704/151224.702198:ERROR:env.cc(226)] The platform failed to initialize.  Exiting.
[0704/151224.705242:ERROR:ptracer.cc(567)] ptrace: Input/output error (5)
[0704/151224.705436:ERROR:ptracer.cc(567)] ptrace: Input/output error (5)
[0704/151224.742590:ERROR:elf_dynamic_array_reader.h(64)] tag not found
[0704/151224.753358:ERROR:file_io_posix.cc(144)] open /sys/devices/system/cpu/cpu0/cpufreq/scaling_cur_freq: No such file or directory (2)
[0704/151224.753382:ERROR:file_io_posix.cc(144)] open /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq: No such file or directory (2)
/snap/brave/166/opt/brave.com/brave/brave-browser: line 48: 11997 Trace/breakpoint trap   (core dumped) "$HERE/brave" "$@"

### Things I tried On Redhat bugzilla they say to run firefox -no-remote. Same issue as before in my case. I found a lot of related answers, but none seem the same. But they have problems with X11, too. So I try some ideas I read there. $XAUTHORITY is empty. $DISPLAY is :1.0. I try xauth list, because ~/.Xauthority exists:

host:1  MIT-MAGIC-COOKIE-1  f91ec0372bd83eb72b686a16530ebb43
[five times the line above]
host/unix:1  MIT-MAGIC-COOKIE-1  f91ec0372bd83eb72b686a16530ebb43

Just in case, I try to set the environment variable:

export XAUTHORITY=c441e3e34e057b5a868d5520dc47e7f4

Still the same error. But echo $XAUTHORITY shows the cookie. Also Gilles states here that ~/.Xauthority is used, when it is not set. The cookie values differ, because I restarted xvncserver and deleted+recreated ~/.Xauthority before I wrote this. Arch wiki lists : xhost +si:localuser:$USER. I did it for my user and root. As far as I understand, this lowers security, but many answers use it as a quick fix. In my case, it throws:

localuser:root being added to access control list
X Error of failed request:  BadValue (integer parameter out of range for operation)
  Major opcode of failed request:  109 (X_ChangeHosts)
  Value in failed request:  0x5
  Serial number of failed request:  6
  Current serial number in output stream:  8

I am not sure if the error even relates to my problem. The same issue is caused by bugs or when the system is build wronlgy . Both things I cannot change at the moment. By now, I am bit clueless: - What is my problem? - How can I solve it? If someone knows a solution it would be great. But my priority is to have a *browser inside a VNC session*, so any kind of workaround would also be appreciated. I also tried to enable SSH X11Forwarding in sshd_config. It did not work. I think this is unrelated, as I use VNC instead of ssh -X option.