I'm not aware of any "racist propaganda" in Firefox, but here is an article about how to select and deselect different content categories for the Firefox Home / new tab page: Customize your New Tab page to hide or display content. You can experiment with the checkboxes and reload the new tab page until it meets your needs.

If you would rather not see Recommended Stories in Firefox, it's easy to hide them. See Customize your New Tab page to hide or display content.

Here's a statement from Mozilla on what's driving the Recommended Stories in Firefox:

"Systemic change -- the real change that this moment deserves, begins with reckoning with America's long history of racial injustice and violence. It requires recognizing how prejudice and injustice continue to corrode the fabric of our society. Platforms have power. During this time, we're using ours to elevate and amplify black and other marginalized voices, and messages that shine a light on these critical issues. This is a starting point that also includes driving change within Mozilla."