Troubleshoot Background Image Problems on Firefox
Continuing on with how to activate View Background images on Firefox, determining if there is a problem with Firefox displaying background images, or if something else is happening is pretty straightforward. Navigate to the website you want to see the background image on. Once it loads, right-click and choose View Page Info from the context menu that pops-up. Select the Media icon at the top. The address of loaded media, including background images, appears here.
If the image you are trying to observe is listed, but does not say "Background" as the image type, that means that as the website has defined it, the image is NOT technically a background image, no matter how it appears on the screen.
If the image is not listed at all, look at the Block Images from website.com checkbox. If it is checked, then Firefox is blocking images from the site due to its configuration. You can easily change this by unchecking the box, or by selecting the Permissions icon and allowing the images there. Obviously, if you were blocking all of the website's images, it would be pretty apparent. However, this screen will also show the web address of images served from somewhere else. This should give you a clue to why the image is blocked in Firefox.
Problems With Displaying Background Images in Firefox
To determine if there is a problem with Firefox causing all background images to be unviewable, use a known good website with a background image. Microsoft's search website Bing.com has a dynamic background image as a way to help distinguish it from its Google search cousin. Assuming Bing.com is not blocked from displaying images, a background image should appear with the search box when Bing.com is loaded. If the image appears, then Firefox itself is not having an issues displaying background images. Furthermore, the View Background Image context menu item should be working.
If Firefox functions correctly on a known good website, then there must be a different issue causing the problem. The most common culprits are Firefox add-ons and extensions. Disable or uninstall any recently installed add-ons and see if the problem goes away. If so, there is a good chance the add-on is causing the issue.
Another common culprit are ad-blocking add-ons. AdBlock Plus is one of the most popular Firefox add-ons. While designed to block Internet advertising, AdBlock Plus functions by means of a pattern matching filter that blocks all elements that match one of the forbidden patterns. Sometimes, an image may be unintentionally blocked. Since AdBlock offers advertising filters that are automatically updated, it is possible that a background image that appeared without problem yesterday, is being blocked today after a filter updated happened in the background. Try disabling your ad blocker, or add the site or element to your whitelist.