The thumbnails on the New Tab page are missing - how to get them back
The Firefox New Tab page shows pictures of the sites you visit frequently. Sometimes, some or all of these images are not displayed. We'll explain why that happens and how to get them back when it's possible.
Turn on the New Tab page
To turn on the New Tab page, click on the gear icon in the upper-right corner of the page and choose Show your top sites from the menu.
Make Firefox create new images for the New Tab page
The new images will be stored as you use the New Tab page to visit those websites again.
Open the New Tab page by clicking the + button on the tab strip.
Click on one of the blank images to open the corresponding website.
Important: Let the website finish loading (wait for the spinning blue loading icon in the tab to stop).
Open the New Tab page again and you will see a new image for the website you just went to.
Repeat this process for the rest of the missing images.
Note: Some websites don't allow images to be generated and saved so they'll show up blank even after doing the steps above. Also, clearing your browsing history (either manually or automatically when Firefox closes) will delete the images.