Based on their logic ads in newspapers aren't ads because customer information isn't shared with the advertiser until they connect with the ad and visit their store.
that's not quite right. newspaper ads are paid placement, while these are not. being paid for placement is an essential feature of advertising. so to differentiate from that, mozilla uses the term "offer" here.
Paid placement is just one model of advertisement. Other well known ones are paid per impression, per click, per action. This is obviously the last one.
I guess Mozilla is confident enough not many people understand what CPA ads are to claim they are not ads.
That's the same DoubleSpeak telemarketers used to say when you asked if they were a telemarketer. "No No, we're just informing you of this new offer in the middle of your dinner with your family."