PS I could access using other browsers.

Hello,

Do you use any add-ons that force HTTPS, such as HTTPS Everywhere? If so, you need to make an exception for sites that are not set up to use HTTPS.

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If this problem is not caused by an add-on:

Possibly Firefox has mistakenly stored an instruction from the server to switch to HTTPS (HSTS). You can remove the file that stores those instructions to see whether that fixes it. Here's how, apologies that I only know the names in English:

Open your current Firefox settings (AKA Firefox profile) folder using either

• "3-bar" menu button > "?" button > Troubleshooting Information
• (menu bar) Help > Troubleshooting Information
• type or paste about:support in the address bar and press Enter

In the first table on the page, click the "Show Folder" button. This should launch a new window listing various files and folders in Windows Explorer.

Leaving that window open, switch back to Firefox and Exit, either:

• "3-bar" menu button > "power" button
• (menu bar) File > Exit

Pause while Firefox finishes its cleanup, then rename SiteSecurityServiceState.txt to something like SiteSecurityServiceState-old.txt (just in case you decide you want to restore it).

Start Firefox back up again. If the site does not once again demand you use HTTPS, then you should be able to access it using HTTP now.

Hope it works. Thank You.