Firefox can’t establish a connection to the server at localhost.

[Cebisa90]

Please first look through the readme and how to use sections to see if your issue is addressed there.

Describe the bug
I am using 4CAT together with Zeeschuimer to collect data from X. It was working fine and then, around 10pm on 13 December 2025, SAST, it 4CAT stopped working. This happened as I was still busy collecting data from X, with Zeeschuimer and creating and
downloading dataset with 4CAT. The options on Zeeschuimer greyed out and it was disconnected afterwards.
To Reproduce
Steps to reproduce the behavior:

1. Go to 'Firefox browser'

2. Click on 'https://localhost/'

3. Scroll down to '..try again..'

4. See error " a message will pop up and the message reads as; Firefox can’t establish a connection to the server at localhost.

   The site could be temporarily unavailable or too busy. Try again in a few moments.
   If you are unable to load any pages, check your computer’s network connection.
   If your computer or network is protected by a firewall or proxy, make sure that Firefox is permitted to access the web.'

Expected behavior
A clear and concise description of what you expected to happen.

4CAT Environment

• How are you accessing 4CAT? If possible, include the 4CAT web interface URL. Otherwise, explain if you are running 4CAT on your own device or accessing it remotely.
• I don't know the version of 4CAT, that I was using and I cannot access it, since 4CAT is not working.
  • The version of zeeschuimer that I am using is v1.13.4
• I am using Docker Desktop.

Screenshots, links to datasets, and any additional context
If your 4CAT is available online and your issue is related to a specific dataset, please post the link.

[Cebisa90]

Please fix it. I tried even with my other laptop, but the issue persists.

[dale-wahl]

What does Docker say? You can click on the containers to see what the logs say. Also, there should be no “S”. It should be http://localhost with no “S”. Unsure if that was a typo. But basically that message implies 4cat is not “on” or there was an error and it was unable to start, but you will have to provide additional information.