Firefox homepage is changed. Now they're displaying a game. How to change it back?

The Firefox homepage is now displaying a game with 'Click Me' call to action button. How to change it back to normal (previous) homepage?

This is by design. Mozilla is supporting a Humble Bundle promotion right now.

Someone asked this question on the Mozilla support forums and received the following response:

That Click Me game is part of the Humble Mozilla Bundle promotion on the default Home Page [about:home], that loads from the Mozilla servers in the "Brand Logo" (DIV) section of about:home. A feature that was first used in Firefox 29 [IIRC] just prior to the start of the Olympic Games.

Also, part of that promotion is addressed in the "Snippet" below the Search Container on the about:home page.

If you want to block the "Brand Logo" section (and the "snippet" below the Search container) from ever being seen again, you can install Stylish and this UserStyle. https://userstyles.org/styles/104673/about-home-hide-snippets-and-hide-brand-logo

Another solution was offered for this as well:

1. Type about:config into the address bar and press Enter.
2. To bypass the warning, press the big button labeled "I'll be careful, I promise!".
3. In the search box, paste browser.aboutHomeSnippets.updateUrl
4. In the search results, double-click browser.aboutHomeSnippets.updateUrl
5. In the "Enter string value" dialog, press the Delete key so that there's no text remaining, then press either Enter or the OK button. As a side-effect, only default tips will be displayed below the search box, because new ones won't be fetched from the web anymore.
6. Type about:support into the address bar and press Enter.
7. Click the Show Folder button. A Windows Explorer window with your profile folder opens. In that window, open the storage folder, then the persistent subfolder.
8. Exit Firefox.
9. Delete the moz-safe-about+home folder.