Seems like the screenshot did not upload, here it is.

Make sure you are not blocking content.

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?

One issue that seems more common lately is Firefox's Tracking Protection feature. When it is blocking content in a page, a shield icon will appear at the left end of the address bar next to the padlock icon. This article has more info on managing this feature: Tracking Protection {web link}

Thank you very much for your time Fred!

I launched Firefox in safe mode successfully, but sadly that did make no difference. My tracking protection has also been turned off.

Start your Computer in safe mode with network support. Then start Firefox. Try Secure websites. Is the problem still there?

http://encyclopedia2.thefreedictionary.com/Linux+Safe+Mode Starting Any Computer In Safe Mode; Free Online Encyclopedia

Thank you for the reply,

What do you mean exactly by try Secure websites?

When on the Mozilla website, look at the address bar. Do you see the padlock? That means the website is secured.

Hello,

For my Youtube website there is a padlock symbol at left of address bar, meaning it is secured. Sadly I did not succeed launching my PC in safe mode with network. I tried multiple ways with network enabled, but in safe mode there was no connection.

Thanks

If you are using WiFi, those drivers would not be loaded in Safe Mode.

As a test, disable your protection programs.

Jyrgen said

Hello all! Perhaps any of you have encountered the same problem. If you try to access Youtube account menu, it will get stuck loading forever. On Google page it is working fine. The problem only exists in Firefox. I disabled all addons, also reinstalled Firefox but with no success. Any ideas? Thanks in advance! Jyrgen

You tube doesn't have the "account menu" so what exactly are you referring to here? I can click through my Library history without problems. Windows 10 Pro FF60.0.2.