That was actually a server-side bug 8 months ago which they not only fixed within 3 days of the issue being reported but followed it up with a hard block against more than 2 displaying at once to make extra sure this didn’t happen again.

If this is what you’re currently seeing then please report it to them. If instead this is an old screenshot then I’ll just agree that Mozilla has certainly suffered many avoidable self-inflicted wounds but this isn’t one of them.

You can disable them, but also I'm pretty sure the default behavior is just to fill extra space if you have less than 8 pinned shortcuts. Your single shortcut is why there are so many ads.

Switching your firefox profile to a firefox fork is super easy peasy squeezy cheesy peas.

You just need to follow the steps for moving your profile in this Firefox support article: https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

When you start librewolf or whatever you switch to (librewolf is what I use) it will have everything from Firefox including whatever your last session was (if you save your session) and all of your history and bookmarks and even addons and UI customization etc.