I've forgot: I use Firefox 77.0.1 but the proble arose with previous versions too.

Did you check with the website's support?

Many site issues can be caused by corrupt cookies or cache.

Warning ! ! This will log you out of sites you're logged in to. You may also lose any settings for that website.

• Delete cookies to remove the information websites have stored on your computer {web link}

• How to clear the Firefox cache {web link}

If there is still a problem, Start Firefox in Safe Mode {web link}
by holding down the <Shift> (Mac=Options) key, and then starting Firefox.

A small dialog should appear. Click Start In Safe Mode (not Refresh).
Did this help?

While you are in safe mode;

Try disabling graphics hardware acceleration in Firefox. Since this feature was added to Firefox it has gradually improved but there are still a few glitches.

How to disable Hardware Acceleration {web link}

Thanks FredMcD. I tried all your suggestions but the problem still persists.

http://kb.mozillazine.org/Images_or_animations_do_not_load

https://support.mozilla.org/en-US/kb/fix-problems-images-not-show

It is possible that (anti-virus) security software is causing the problem.
Try to disable security software temporarily to see if that makes a difference.

I tried, no change...

Hello Masss,

Would you try this please :

Type or paste in the address bar   about:config  and press Enter
(ignore the warning)

Type or paste in the search bar :

privacy.resistFingerprinting.autoDeclineNoUserInputCanvasPrompts

and set its value to   false

If you get a permissions prompt asking to allow HTML5 canvas image data :

Click   "Allow"

Any luck ?

Probably a redundant remark, but if allowing HTML5 canvas image data does the trick, then the preference on the   "about:config"   page can keep its default value of   "true".

Do you see the canvas notification icon () on the location bar when this happens ?

• chrome://browser/skin/notification-icons/canvas.svg