How I can prevent pages only opening 3/4 size so the previous page is showing behind the open one?

You can maximize your browser window to use it in full-screen. To display all pages properly, QuickBooks Online requires these settings:

• Screen resolution set to 1024x768 or higher
• Dots-per-inch (DPI) set to Normal or 100%

Also, you can modify your browser's shortcut properties to force it to open maximized. Here's how:

1. Right-click your browser icon on the Desktop or Taskbar.
2. Select Properties from the menu.
3. Look for the Run option and change the drop-down menu to Maximized.  
4. Click Apply, then OK.

Feel free to reply below if you have any other questions.