Each browser window contains a source list, a records list, a record viewer, and a toolbar. Drag the split bars to resize the different portions of the window. Double-click a split bar to collapse it entirely. Hold down the Option key while dragging a split bar to grow or shrink the window as you drag.
You can use the Tab key to move between the different panes using the keyboard. When editing in the record viewer, you may need to type Control-Tab rather than Tab (which will insert a tab character into the document).