Let me walk you through the steps in adjusting your display setting while using QuickBooks Online. Here are the steps to follow:
Google Chrome
On your upper right, click on the three-dotted menu icons.
From that icon, you can find the Zoom option.
Hit the minus (-) icon to zoom out and make your page smaller, or press the plus (+) to zoom in and make your page larger. The page should be set to 100% or lower to display the whole page.
Firefox
If your page is larger than the browser window, press the Ctrl key on your keyboard and minus (-) key repeatedly to zoom out the page and the Ctrl and plus (+) keys to make your screen larger.
You can also hold the Ctrl key and move the wheels on your mouse forward to make your screen bigger or move the wheels backward and hold the Ctrl key to make it smaller.
The steps mentioned above will work on any pages that are too big or too small for your liking. These steps will also work even if you're using other than QBO.