Are you actually trying to resize the window, or just the text?
To resize text in your web browser, press Ctrl and + (bigger) or Ctrl and - (smaller) together. Pressing Ctrl and 0 takes you to the default size.
To resize text in general, change your screen resolution. (Right-click on your Desktop and select 'Properties'. Click the 'Settings' tab and move the slider. Increasing the resolution makes text smaller and vice versa. Click 'Apply' and 'OK').
To adjust the size of a window, click-and-drags its edges.
Chris