Make sure you are not blocking content.

Start Firefox in Safe Mode {web link}

A small dialog should appear. Click Start In Safe Mode (not Refresh). Is the problem still there?

https://support.mozilla.org/en-US/kb/enhanced-tracking-protection-firefox-desktop

You can create a new profile as a quick test to see if your current profile is causing the problem.

See "Creating a profile":

• https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles

If the new profile works then you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over problems.

• https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

- - - - Boot the computer in Windows Safe mode with network support to see if that has effect in case security software is causing problems.

• https://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/
• https://www.7tutorials.com/4-ways-boot-safe-mode-windows-10

FredMcD: The thumbs were still missing in safe mode.

cor-el: When I created a new profile, the thumbs issue was not there. Now the next problem is what I should move from one profile to the other that will address this specific issue.

https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles

I take it the new profile is working without a problem, yes?

When you are ready, we can start moving parts of your old data and Copy it to the new profile.

First; open your file browser to the New profile;

Type about:support<enter> in the address bar.

Under the page logo on the left side, you will see Application Basics. Under this find Profile Folder. To its right press the button Show Folder. This will open your file browser to the current Firefox profile. Now Close Firefox.

Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder

Linux: Under the page logo on the left side, you will see Application Basics. Under this find Profile Directory. To its right press the button Open Directory.

Second, open another file browser to the Old profile. You should see it on the directory "tree" in the first file browser. Right-click on that folder and select Open In New Window.

Warning ! ! Only Copy the files you are told. We will avoid anything that might cause problems. Here is the list of files;

cookies: cookies.sqlite Do not bother. Cookies will be created when you return to the website. However, you will have to log in everywhere. And you may lose any settings that websites store on your computer.

extensions(add-ons, themes): it would be better to download them fresh. If you need to remember what add-ons you had, open the extensions sub-folder and look at the .xpi files ++++++++++++++++++++++++++++++++ logins.json and key3.db [v58+]key4.db : These are the password files. Copy Both !

persdict.dat : custom dictionary - words you added to the dictionary

mimeTypes.rdf [v55+]handlers.json : What to do with what type of file.

places.sqlite : History and Bookmarks.

prefs.js : Your settings. Note: If you were having problems, this could be contaminated.

cert8.db [v58+]cert9.db and possibly cert_override.txt : Stores all your security certificate settings and any SSL certificates you have imported into Firefox. If removed, the cert8.db, cert9.db file will be replaced.

search.json.mozlz4 : file stores the user-installed search engines that are available in the Firefox v47+

search.sqlite file and searchplugins folder store the search engines that are available in the Firefox Search bar before Firefox v47 +++++++++++++++++++++++++++++++++++++++++++++++++ Copy these files from the old to the new. You may get a message that the files already exist. Choose to over-write for each file.

FredMcD: All done, but it didn't accomplish anything. Still seeing no thumbs on main page, and only in first few groups on subscribed channels.

Did you install/copy any extensions in the new profile ? Files like prefs.js are also best left out.

cor-el: As to extensions, not yet; I kept a list of them, tho. I did copy prefs.js; that'll get deleted shortly.

EDIT: Deleting prefs.js reset a bunch of things, but didn't solve the missing thumbs issue.

Hello   Dale_Latimer,

Stab in the dark, but would you check this please :

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

Type in the search bar and look for the preference :

image.webp.enabled   and make sure its value is set to   true.

If you had to change the value, then close and restart Firefox.

Any luck ?

Type in the search bar and look for the preference :
image.webp.enabled   and make sure its value is set to   true.
If you had to change the value, then close and restart Firefox.
Any luck ?

That was already set to true.

I bet this is   "one of those YouTube things"   that will suddenly fix itself .....

There are numerous threads   (especially on Reddit)  about this problem, and has been for years.

But as you mentioned that the problem isn't there in a new profile;   that might be worth looking into some more.