Firefox 75 switched from the button to show frequently visited pages to automatically dropping down your first 8-10 Top Sites from the Firefox Home / new tab page. The list is managed on that page, and can't be modified from the address bar drop-down.

If the Top Sites list is not helpful, you can switch it off on the Preferences page, Privacy & Security panel, Address bar section. To show a frequently visited pages list similar to the old one, you can either:

• type a space into the bar
• turn on the history filter by clicking the tiny clock icon on the bottom row next to the search engine buttons (or typing ^ into the bar)

If you want a frequent URLs list without typing anything, I have an add-on for that, but its list appears outside the address bar drop-down. https://addons.mozilla.org/firefox/addon/show-history-top-sites-button/

I like that FF automatically drops down your first 8-10 Top Sites. The problem I am having is that the Top Sites are not updating. It has remained the same for the last few months with sites I don't even go to anymore.

It could be that sites are pinned there. Do you notice a little "push pin" icon in the lower right corner of Top Sites when listed on the address bar drop-down?

You can manage that list -- unpinning, dismissing, adding URLs -- on the built-in home page (about:home) or new tab page (about:newtab) as described in this article:

Customize your Firefox New Tab page

They are not pinned

You still can "dismiss" unwanted sites from the new tab page's Top Sites section. That adds them to a block list so they don't appear there again.

Top sites not even showing up when I create a new tab.

If you use Sync then best is to disconnect Sync temporarily during troubleshooting.

This can be caused by a problem with the places.sqlite and favicons.sqlite databases in the Firefox profile folder.

• use "Verify Integrity" button on the "Help -> Troubleshooting Information" (about:support) page

If errors are reported with "Verify Integrity", close and restart Firefox or reboot and retry.

If "Verify Integrity" cannot repair places.sqlite, rename/remove all places.sqlite and favicons.sqlite files in the Firefox profile folder with Firefox closed. Firefox will rebuild places.sqlite and restore the bookmarks from a recent JSON backup in the bookmarkbackups folder.

• keep a backup copy of places.sqlite in case a new places.sqlite database has to be created

You lose the history when a new places.sqlite is created.

See also:

• https://support.mozilla.org/en-US/kb/Bookmarks+not+saved#w_fix-the-bookmarks-file
• https://support.mozilla.org/en-US/kb/fix-bookmarks-and-history-will-not-be-functional

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

• Help -> Troubleshooting Information -> Profile Folder/Directory:
  Windows: Open Folder; Linux: Open Directory; Mac: Show in Finder
• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data

has not helped. I've also uninstalled and reinstalled.

Top sites not even showing up when I create a new tab.

Is the Top Sites section enabled on the about:home / about:newtab page? You can check that on the Preferences page: Customize your New Tab page to hide or display content.

So it's gotten better. When I changed my "Homepage and new windows" from custom to Firefox Home, the sites showed up on a new tab and I am able to edit them. When I change it back to custom they are staying there. It is still not updating the top sites automatically as it should.

Are you comparing to the list generated by typing a space or ^ in the address bar? That history-based list should feed into the Top Sites and change it over time (except for pinned items that can't be moved). I can't say I fully understand the ranking; there's a lot of math: https://developer.mozilla.org/docs/Mozilla/Tech/Places/Frecency_algorithm

Appears there is 3 different behaviors now. When I used to just click on the address bar I would get a list of top sites listed in order of most visited. That is remaining static now. When I type in ^ it seems to result in most visited order. When I type space is seem to result in recent history but not really sorted. Did the behavior of just clicking on the address bar change?

ed71 said

Top sites not even showing up when I create a new tab.

Is the Top Sites section enabled on the about:home / about:newtab page? You can check that on the Preferences page: Customize your New Tab page to hide or display content.

Appears there is 3 different behaviors now. When I used to just click on the address bar I would get a list of top sites listed in order of most visited. That is remaining static now. When I type in ^ it seems to result in most visited order. When I type space is seem to result in recent history but not really sorted. Did the behavior of just clicking on the address bar change?

Before Firefox 75, I don't think clicking in the address bar did anything automatically, but there was a little icon to open a frequently visited URLs list. Starting in Firefox 75, clicking in the bar automatically opens a list showing the first 8-10 Top Sites from the new tab page.

The ^ list draws purely from history, and is in "most frecent" order.

When this change first occurred, users compared that with the spacebar list and found that the spacebar led to a closer match to the old list. However, it's certainly possible that the secret sauce behind the order of items on these lists has changed since then. For me, the only difference is in the order of items 2-4.