If you have set the number of entries in the address bar popup in Firefox too high after clicking in the address bar, it can happen that the lower entries are no longer displayed. In this case you need a CSS code to create an additional scroll bar.
This is what it looks like by default if you have too many entries:

The entries displayed extend beyond the edge of the screen at the bottom and you cannot see the other entries.
Note:
I had already given a CSS code for this here , but it no longer works in the current version of Firefox.
(You can change the number of entries in this popup in about:config under the value browser.urlbar.maxRichResults )

Regarding about:config I had already written an explanation here.
about:config explanation
Create userChrome.css and userContent.css
A notice:
If you are using one of these files for the first time, you must also enter the value in about:config:
toolkit.legacyUserProfileCustomizations.stylesheets
switch to true.
I have already described how this is done here:
reuse userChrome files
And here is the explanation of how to do it with the CSS code.
First we go to the Firefox profile folder and open the chrome folder we created ourselves.
Then open the userChrome.css file in the chrome folder.
We now enter the following CSS code in this file:
/* display a scroll bar for address suggestions in the urlbar */ :root { /* value must be identical in about:config = browser.urlbar.maxRichResults */ --ac_popup_number_of_results: 80; /* The higher the value above, the smaller the px value must be */ --ac_popup_maxheight: calc(6px * ( var(--ac_popup_number_of_results) + 1 )); --ac_popup_height: calc(400px * var(--ac_popup_number_of_results)); } /* Maximum entries that are displayed without scrolling */ .urlbarView:not(.megabar) { height: var(--ac_popup_height) !important; max-height: var(--ac_popup_maxheight) !important; } /* Margin at top and bottom of address listing */ #urlbar-results { margin-top: 1px !important; margin-bottom: 3px !important; } /* Scrollbar and address listing position */ .urlbarView:not(.megabar){ overflow-y: scroll !important; margin-top: -1px !important; margin-bottom: 1px !important; } /* Disable urlbar extension */ #urlbar[breakout][breakout-extend] { top: calc((var(--urlbar-toolbar-height) - var(--urlbar-height)) / 2) !important ; left: 0 !important; width: 100% !important; } #urlbar[breakout][breakout-extend] > #urlbar-input-container { height: var(--urlbar-height) !important; padding-block: 0 !important; padding-inline: 0 !important; } #urlbar[breakout][breakout-extend][breakout-extend-animate] > #urlbar-background { animation-name: none !important; } #urlbar[breakout][breakout-extend] > #urlbar-background { box-shadow: none !important; } } #urlbar[breakout][breakout-extend] > #urlbar-input-container { height: var(--urlbar-height) !important; padding-block: 0 !important; padding-inline: 0 !important; } #urlbar[breakout][breakout-extend][breakout-extend-animate] > #urlbar-background { animation-name: none !important; } #urlbar[breakout][breakout-extend] > #urlbar-background { box-shadow: none !important; } } #urlbar[breakout][breakout-extend] > #urlbar-input-container { height: var(--urlbar-height) !important; padding-block: 0 !important; padding-inline: 0 !important; } #urlbar[breakout][breakout-extend][breakout-extend-animate] > #urlbar-background { animation-name: none !important; } #urlbar[breakout][breakout-extend] > #urlbar-background { box-shadow: none !important; }
And this is what the code looks like in the userChrome.css file:

The value for browser.urlbar.maxRichResults can be changed or adjusted as desired.
Then close and save the userChrome.css file and restart Firefox for the change to take effect.
And this is what it looks like with the new additional scroll bar:

Scrollbar in Firefox