Excuse me for commenting, but the Ad Block ads are just as annoying and persistent as the ads which you are proposing to block for a fee. Please stop them! I can't even operate certain web sites properly because the lower banner overlays key dialogue boxes.
In the realm of high pressure sales, this is surprising and disappointing for an organization like Mozilla. Please put this promotion effort under the control of someone with a more experienced and measured operating pattern. Or at least give us the option to hide the banner. If such an option exists, I have not been able to find the switch to activate it.
As superuser said, looks you have an ad-blocking extension installed, check your Extensions and Themes. In this case, if the extension allows it, you can add certain websites to exclusions to keep your extension or uninstall it.
I suggest trying these steps to remove unwanted extensions from Firefox:
If the extensions reappear after restarting your computer, you may need to run a malware scan. To scan your system, use free tools such as Malwarebytes or Windows Defender. Consider updating your security software to the most recent version and keeping it turned on at all times.