Previously in Firefox 77 if the browser.urlbar.maxRichResults was set to some value, let's say 20, then the 20 most recent urls would be shown in the urlbar dropdown when you clicked on the urlbar. Now only 8 are shown. However, as soon as you start typing it will show 20 matches to what you've typed. This pref now appears to only work in some situations, rather than in all situations.

This is because the urlbar now shows "top sites" when you click it instead of history, the same top sites shown on the new tab page. By design, the urlbar shows the same number of top sites that the new tab page does. You can add more top sites rows to the new tab page in order to show more results in the urlbar.

We know that the connection between the urlbar and the new tab top sites isn't clear right now, and bug 1628025 covers that.

(In reply to Drew Willcoxon :adw from comment #1)

By design, the urlbar shows the same number of top sites that the new tab page does.

Actually it shows that number or maxRichResults, whichever is smaller.

I don't have any "top sites" selected on the new tab page (I prefer just to use about:blank on new tabs). It just shows historical urls (presumably sorted by frecency).

Also, I just double-checked. If I set the new tab page to use Firefox Home, it shows two rows of "top sites", which is 16 individual items, not 8.

Sorry, I didn't realize this was fixed in 79, in bug 1631848, but you're probably running 78. I'll mark this as a dupe of that. Bug 1628025 covers making the connection more clear, as I mentioned.

"Top sites" just means your top visited sites mostly, plus any sites you pin to the new tab page. It's basically a list of your most frecent sites. By new tab page, I mean about:newtab, regardless of whether you use it for your new tab page.