Can you post a screenshot from another browser showing what you're talking about?

If you use extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) that can block content (Adblock Plus, NoScript, DuckDuckGo PE, Disconnect, Ghostery, Privacy Badger, uBlock Origin), always make sure such extensions do not block content.

• make sure your extensions and filters are updated to the latest version
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

You can try these steps in case of issues with webpages:

You can reload webpage(s) and bypass the cache to refresh possibly outdated or corrupted files.

• hold down the Shift key and left-click the Reload button
• press "Ctrl + F5" or press "Ctrl + Shift + R" (Windows,Linux)
• press "Command + Shift + R" (Mac)

Clear the Cache and remove the Cookies for websites that cause problems via the "3-bar" Firefox menu button (Settings), click the padlock icon (Clear cookies and site data) for the domain in the selected tab.

"Remove the Cookies" for websites that cause problems:

• Settings -> Privacy & Security
  Cookies and Site Data: "Manage Data"

"Clear the Cache":

• Settings -> Privacy & Security
  Cookies and Site Data -> Clear Data -> [X] Cached Web Content -> Clear

• https://support.mozilla.org/en-US/kb/clear-cookies-and-site-data-firefox
• https://support.mozilla.org/en-US/kb/how-clear-firefox-cache

Start Firefox in Troubleshoot Mode to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration or if userChrome.css/userContent.css is causing the problem.

• switch to the Default System theme: "3-bar" menu button or Tools -> Add-ons -> Themes
• do NOT click the "Refresh Firefox" button on the Troubleshoot Mode start window

• https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

You can check for issues with Enhanced Tracking Protection. Firefox shows a purple shield instead of a gray shield at the left end of the location/address bar in case Enhanced Tracking Protection is blocking content.

• click the shield icon for more detail and possibly disable the protection

You can check the Web Console for relevant-looking messages like blocked content.

• https://support.mozilla.org/en-US/kb/enhanced-tracking-protection-firefox-desktop
• https://support.mozilla.org/en-US/kb/total-cookie-protection-and-website-breakage-faq
• https://support.mozilla.org/en-US/kb/trackers-and-scripts-firefox-blocks-enhanced-track

No add-ons installed, cache and cookies were cleared, but still this box of "latest videos" (on the screenshot below) not showing.

I see it in YouTube Studio. see screenshot Did you try in Safe Mode?

What do you see if you right-click in that area and click Inspect ?

• https://firefox-source-docs.mozilla.org/devtools-user/page_inspector/how_to/examine_and_edit_html/

Any relevant-looking messages in the Web Console ?

• https://firefox-source-docs.mozilla.org/devtools-user/web_console/

jonzn4SUSE, yes, tried a safe mode, but it doesn't change anything. cor-el, no errors or something like that weren't there.

Just now the box started showing, but noticed that if it loads from previous session in Analytics tab -- the box isn't there, but if it loads from, for example, Content tab and then I go to the Analytics -- works fine. UPD: when reload the Analytics page -- box disappears, although was there just before

Also, earlier the box was showing but when clicking on it -- just disappears

Windows home or pro? If pro, try this. https://www.howtogeek.com/399290/how-to-use-windows-10s-new-sandbox-to-safely-test-apps/

Sometimes pages or tabs within a page are generated through JavaScript and in such a case you can't reload the page and you may have to select the tab again.

Have tried everything suggested above, but nothing helps :(

jonzn4SUSE, could you please reload the page Analytics in YouTube Dashboard and see if the box is stiill appearing? Once I reload the page Analytics, the "Latest Content" disappears, and I should go to Content, reload there and switch back to Analytics, then it works, but.. :(

I see the same issue on Win7. It was there, but after refreshing the page it's gone. Seeing same behavior in Chrome so it doesn't appear to be a browser issue.

Signed out and cleared cache. After signing back in it's there. see screenshot Again, refresh and it's gone. YouTube issue.

jonzn4SUSE , thank you very much for checking it from your side. :) Also installed ESR version and Portable, checked there, but also nothing changes :(

Okay... If no further questions just mark it as resolved to get it off our long list of issues. Have a nice day.  ;-))