An interesting side effect of an earlier policy means that the sponsored ads for extensions will not be able to be blocked. Firefox extensions are prevented from operating on AMO. This is or was to ensure malicious addons can't interfere with its operation.

Now, it also means Mozilla is in the enviable position of offering ads to Firefox users which can not be blocked by Firefox ad blocking extensions.

Put another way, if you want to browse AMO ad free, you will need to use a different browser.