After your Toad for Oracle installed in a new computer, you may see a strange layout in Session Browser like mine.
Toad for Oracle - Session Browser Vertical Layout
It's a vertical layout by default in session browser.
To flip session browser layout from vertical to horizontal, we can click on "Flip Layout" icon at top of the panel.
Toad for Oracle - Session Browser Flip Layout Icon
After flipping it, we saw a horizontal layout of session browser.
Toad for Oracle - Session Browser Horizontal Layout
To revert the layout, you click the icon again.