Type about:config in the Location Bar and hit Enter.

Type browser.urlbar.maxRichResults in the Search bar at the top.

Then right-click that pref and select Modify. Enter the number you want and hit OK. The restart Firefox to set that pref.

I don't mean the URL bar's number of items. I'm talking about when you click the word "history" (or alt-s).

When you go to history section you get a history option in bottom of that you get a link "show all history" click on that you get a popup which shows the full browsing history.

That's true, but I'm asking if there's a way to change the number of results in the pulldown menu. There used to be in older versions -- did they remove it?

That is not possible. That value of 15 is hard coded and can not be changed. AFAIK then this has always been this way (it has been 10 in Firefox 3 versions). You can open the history in the sidebar to see more history items.

• You can toggle the Bookmarks sidebar on/off via "View > Sidebar > Bookmarks" or "Ctrl+B" (Command+B on Mac)
• You can toggle the History sidebar on/off via "View > Sidebar > History" or "Ctrl+H" (Command+H on Mac)

Current Firefox releases have a "Show > Sidebars" button in the Customize palette.

• "3-bar" Firefox menu button > Customize
• View > Toolbars > Customize

There is a "View Bookmarks Sidebar" item in the "Show your bookmarks" drop-down list and a "View History Sidebar" in the "Show your history" drop-down list.