Hey, I never noticed that before.

For the large site icons, a size of 256x256 pixels works well. I set that up here as an experiment:

• Site: https://www.userchrome.org/
• Icon: https://www.userchrome.org/img/Fxcss_256.png

I don't know the parameters for what other kinds of images can be added, but I tested using this sunset photo. After pasting the URL and clicking Preview, and a few moments of a progress dot going back and forth, I was able to see it in the overlay. I canceled after that.

https://www.jeffersonscher.com/ttw/wp-content/uploads/2017/02/BakantiangBay-SunsetYoga-2124_1600.jpg

Does that one work for you?

Imgur and some other image sites may limit how you can embed images on other sites, so if those hosts don't work for this purpose, you might try something that is less restricted like a shared folder on OneDrive or Google Drive.

Hello, and thank you for the quick response.

Unfortunately testing with your photo yields the same results, after pasting the URL and pressing Preview I get "Image failed to load. Try a different URL." aswell.

Since that image works for you, it must be my Firefox causing this problem. Should I try restoring Firefox to its default settings or is there something else I could try since I'd prefer not doing that.

Do all the images load normally in a regular tab, the only problem is on the new tab page?

Could you check for error message in the "Browser Console" that could be related to this problem?

You can open the separate Browser Console window using either:

• "3-bar" menu button > Web Developer > Browser Console
• (menu bar) Tools > Web Developer > Browser Console
• (Windows) Ctrl+Shift+j

Click the trash can icon at the upper left to clear the window, then switch back over to your main window and try the image Preview again.

Then switch back over to the console window. Did Firefox log anything more explanatory about the problem?

More info on the Browser Console: https://developer.mozilla.org/docs/Tools/Browser_Console

Yes, just opening the URL in a new tab loads the images just fine, only trying to add it as a custom image makes problems.

There aren't any error messages being logged when trying to add those custom images either unfortunately.

I decided to use the Refresh Firefox option in about:support and its working as it should now. Even after I setup all settings and addons as they were before. Maybe there was some setting in about:config that caused this, I am not sure.

Anyway thank you for your help.

I'm glad to hear that worked. Custom settings in about:config are mostly saved in the prefs.js file in your profile folder. If you get curious, you could compare the one in your Old Firefox Data folder on your desktop with your currently live one. This article will help you get to your profile folder:

Profiles - Where Firefox stores your bookmarks, passwords and other user data

I generally use this program for text file comparisons: http://winmerge.org/

There will be lots of differences related to dates/times, but hopefully those won't be too distracting.

I found out what was causing this issue! Quite a while back I had added "browser.pagethumbnails.capturing_disabled" and set it to true because I wanted to stop Firefox from showing screenshots of websites when the Top Sites Page replaced the old about:newtab.

Testing it out now what seems to happen is, if you try to add a custom image while this option is enabled, it saves a 0byte .png file in the thumbnail folder of your profile folder in Appdata/LOCAL, not the one in Roaming where the prefs.js is located.

Even if you disable/remove the preference after trying to add an image and restart Firefox, trying to add the same image will still fail since Firefox tries to save it under the same name as the 0byte file.

So what you will probably have to do is to navigate to the thumbnail folder and delete what is inside.

I hope this is helpful in case anyone ever has the same problem.

Hi, always make a Notepad list of the changes you make in there. https://support.mozilla.org/en-US/kb/customize-new-tab-page