For months I have been using the Developer Toolbox (Inspector) to develop and test changes to my userChrome.css. Suddenly, today, when I try to open it, I get an error "Component returned failure code: 0x804b000d (NS_ERROR_CONNECTION_REUSED)" - see attachment for screenshot of entire error message (why doesn't the window allow me to copy and paste?) However, there is no such problem on new PC I am setting up I am used to getting a dialog asking me to accept the connection, but I am not getting that today. It just silently fails. Did I accidentally reject this connection in the past? If so, is this remembered? How would I "un-remember" this? I have checked several advanced settings that I have read about: * devtools.toolbox.sideEnabled is set to true * devtools.debugger.remote-enabled is set to true * devtools.debugger.remote-port is set to 6000 * devtools.debugger.remote-host is set to localhost * devtools.debugger.prompt-connection is set to true I tried restarting in ''''''Troubleshoot Mode'''''' I tried downloading and installing over the existing install. I have tried completely uninstalling and re-installing. No help. I have tried creating a new profile and using that. No help. I have tried with my VPN connected AND disconnected. I have restarted my system. No Help. Thunderbird is allowed to communicate through the Winders Defender Firewall. I have no other Firewall or Anti-Virus software other than Windows Defender. I have tried with the firewall both OFF and ON. TB 102.6.1 (64-bit) on Windows 10, both at latest updates. I am trying to think of what might have changed in the past few days. I know I HAVE NOT changed Anything in advanced Config. I think I got 102.6.1 a few days ago.