When I open a new tab, there are three certain preview thumbnails which are always empty, and there is no way I can make them show up again. They did work in the beginning, but at some time the three previews vanished and never came back. I have already tried to empy the cache and reload the sites as suggested here, but the thumbs are still empty. It's always the same three URLs where this happens. I have also cleared the history, opened the sites again and dragged the items from the history menu into a thumbnail - same result.
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The pages may be send by the server with a no-cache or no-store header preventing Firefox to store that pages in the cache.
Firefox will only generate thumbnails if the page is in the cache.
The thumbnails on the about:newtab page are generated from the cache, so if the page is not in the cache or otherwise can't or won't (secure pages) be rendered as a PNG image then you will get an empty box.
- Do not use Clear Recent History to clear data like the cache and the history when you close Firefox
If there is no history then you get an about:newtab page with empty boxes (no URLs).
- bug 756881 - New tab thumbnails not displayed (or old images displayed) for Facebook, Twitter (sites using Cache-Control no-store)
How can I find out if this is the case? I found no "no-cache" tag or something like that in the HTML source. I used to think it worked on another computer, but now I cleared its cache as well and the previews are gone there too. So it could ineed be a general problem with the sites.
You can open the Web Console (Web Developer > Web Console;Ctrl+Shift+K) and click the entry of the main (index) page to inspect the response headers.
You can reload web page(s) and bypass the cache to refresh all files files.
- Press and hold Shift and left-click the Reload button.
- Press "Ctrl + F5" or press "Ctrl + Shift + R" (Windows,Linux)
- Press "Cmd + Shift + R" (MAC)
I couldn't find the relevant headers in the web console straightaway, but I found a web site that displays these headers for a given URL. It looks as if the no-store header is the culprit. All the pages without previews have it.