I had to download your picture, Then convert it to see what you were on about.

I have not seen anything like this.

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).

Is the problem still there?

Update your Flash Player Note: Windows users should download the active_x for Internet Explorer. and the plugin for Plugin-based browsers (like Firefox).

Note: Windows 8 and Windows 10 have built-in flash players and Adobe will cause a conflict. Install the plugin only. Not the active_x.

Flash Player Version: 21.0.0.242 Flash Player (Linux) Version 11.2.202.621

https://get.adobe.com/flashplayer/ Direct link scans current system and browser Note: Other software is offered in the download.

https://get.adobe.com/flashplayer/otherversions/ Step 1: Select Operating System Step 2: Select A Version (Firefox, Win IE . . . .) Note: Other software is offered in the download.

See if there are updates for your graphics drivers https://support.mozilla.org/kb/upgrade-graphics-drivers-use-hardware-acceleration

Security Issue: Update your Adobe Reader Version 2015.016.20039 Note: Other Software is offered in the download.

In safe mode it looks the same. I have also tried a clean install and also delete the profile folder(C:\Users\user\AppData\Roaming\Mozilla\Firefox\Profiles\0ltzpl9n.default)

PS: I couldn't add image in the post(I waited a lot to load and nothing happened); that is why I post the link for the screenshot.

I've called the big guys to help you. Good luck.

Start your Computer in safe mode with networking. Then start Firefox. Try Safe websites. Is the problem still there?

Starting The Computer In Safe Mode;
Free Online Encyclopedia

Yes...In Windows SafeMode it looks ok. How to fix this also in Normal mode? :d

That means one of the other programs on your computer is the cause. As a test, disable your protection programs.