By "custom urls" do you mean that you have 4 tabs which are saved and reopen when you restart the browser? I currently have 9 such tabs and if I open a new window, it contains only a blank tab.

Are you referring to a home page and new tab page?

Thanks, Terry. I've uploaded an image showing my current settings (the cropped "Homepage and new windows" field includes the four pipe-delimited URLs).

I couldn't find any other obvious way to use these elements to get the basic behaviour I wanted (reopening a set of tabs when I reopen the Mozilla profile), but it is overenthusiastic and always opens them whenever I create a new window via Ctrl-N.

I'm probably missing something obvious...

If you open a new window (Ctrl+Shift+N) then this window is populated with the home pages. The only way to open a blank new window is setting the home pages to a blank page.

If you only want this for the pages that open if you start Firefox then add those pages to the target line in the Firefox desktop shortcut. You can have the use a bat/cmd file with the start command if you exceed the maximum length of this field.

• start "" "<path_to_firefox>\firefox.exe" -url URL1 URL2

Thanks cor-el. I was expecting the default behaviour to work like Chrome's startup pages (or to locate an extension that mirrored that), but this does just what I need, at least for my main profile.

Note to self, in case I ever find myself here again: Holding shift while right-clicking items in Windows 11's dumbed-down taskbar allows you to get to the Properties dialog.