To create separate, side-by-side browser windows for FamilySearch and The Family History Guide,
Open FamilySearch in a browser tab.
Open The Family History Guide in a new browser tab.
Click the tab for The Family History Guide and slowly drag it to the left (or right) until it becomes its own window. (You may need to make your browser window smaller or pull it to the left to provide room.)
Resize the two browser windows and arrange them side by side.