FF forum is for Enduser of FF Browser problem not for site issues that is to contact their webmaster for the site your having issues with.

Hi Antonio, Unfortunately, that link requires a password, so I can't test it, but we can provide some general troubleshooting tips you can try.

First, let's try something simple, like clearing your cache and cookies.

1. Click the Library button and choose History.
2. In the History menu, choose Clear Recent History.
3. In the Time Range to clear drop-down, select Everything.
4. Click the arrow next to Details to display the list of items that can be cleared.
5. Select both Cookies and Cache.
6. Click Clear Now.

Tell us how it goes. ☺️

In your system details I saw something way more serious :

You have a browser hijacker, called FromDocToPDF, malware, that you will need to get rid of.

Go to the Firefox menu (≡) => Add-ons => Extensions

( Mac  : Command + Shift + A)

Remove that 'FromDoctoPDF' and look for any other unfamiliar or suspicious looking extensions.

When you find any : remove them.

Do the same here : for Windows => Control Panel for Mac and Linux => System Preferences

However : most malware will be 'hiding' somewhere , so let's run malware scans (even though you already have run some) :

Further information can be found in this article : https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware?cache=no

Run most or all of the listed malware scanners. They all work differently - what one program doesn't pick up, the other might.

Also see : https://www.wintips.org/how-to-remove-fromdoctopdf-toolbar/

Especially for Mac : https://www.malwarebytes.com/mac/

And : https://malwaretips.com/blogs/remove-mac-os-x-virus/