There are plenty of Firefox forks in the F-Droid store. I use Fennec which natively supports everything you mentioned.
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Or Ironfox. I installed Ironfox after a Fennec recently shit the bed and didn't work at all. It's good, too.
Mozilla: "Firefox is losing millions of users"
Also Mozilla: "let's alienate our most loyal users with World Cup ads in Firefox!"
FFS guys.
And Ai, don’t forget the ai. Really sad directions being taken by literally the only chrome alternative browser.
I'm not sure how Firefox can know the difference between a loyal and casual user, but if such thing even exist it doesn't matter to Mozilla.
Let's be real, how many % of the browser market is owned Firefox? 3%? Loyal users would be like 0.5% or even less.
They care about money (and is fine, they need it to maintain the project) and attracting new casual users, and this is the kind of thing that do both: Not sure if FIFA sponsored Mozilla but looks like, and casual people will open Firefox just to see the World Cup results
And even so, you can just turn it off, I guess
Hmm I've never once seen an ad but I have all the home page stuff turned off. 
I tried toggling them and none of them showed anything like you screenshot.
I'd also think turning off any setting with the word "sponsor" might work

Edit: realized the screenshot is supposed to be a notification... I also haven't ever seen a notification outside of functional ones, and I don't see any setting about it anywhere...
Similar to me, and haven't seen that ad. I also checked that all notification channela are enabled for me.
There is a setting: Data collection -> Studies. That may be the reason for OP. But if data collection is disabled then it also disables studies:

For me there's a class of notification labeled "Marketing". It's disabled now but obviously wasn't when I got the notification, presumably on account of it being new.

Wow that is egregious. I don't have that but like the other person mentioned I have studies disabled so maybe it's part of that at first
Does Mozilla get paid by Fifa for this?
Also I have Fennec from f-droid and haven't received anything world cup related
Settings > Homepage 
I've been getting them in Android auto and want to know how to disable that shit also. (Unrelated to Firefox)
Couldn't give less of a fuck about who scored a goal.
Get Fennec or IronFox, they're Firefox forks so you get all the extensions you're used to minus the BS.