As posted in your other thread, if you want to keep a present window open, you need to open a new window. There are several ways of doing this that are mentioned in the other thread.
It is not possible to have the content from one webpage showing when you have another webpage open. If you want to look at two pages at once, use the button between the X and the _ to resize both windows. You may have to manually reshape the window by moving the mouse to the side or bottom or top of the window, pressing down on the left button and moving the side, top, or bottom while holding down the mouse button.
Note: If you have several windows open, they will pile up on each other in the task bar. There will be a number, followed by the program identification, followed by a little arrow. Click on the little arrow, and you will see the titles to all the webpages you have open. Occasionally, a program or webpage will disappear from the taskbar. That doesn't necessarily mean it's closed. Open Taskmanager by pressing Ctrl + Alt + Delete. Click on the applications tab and you will see the names of all the webpages and programs you have open. Right click on the name of the website or program you don't see and click on "bring to front" in the menu that comes up. The website or program will now reappear in the task bar, and it will be on top of any other windows you have open.
By the way, you won't mess up your computer by installing Firefox. I have both IE and Firefox. I usually use Firefox at home excepting when I'm updating my computer. You would only mess up your computer if you uninstalled