Apple Mail display

When an email arrives, let's say I click on a web site link. Normally a new page displays at the same size as the Mail page. Suddenly the new page displays at about half size, a size which cannot be changed, nor does it have the familiar red, yellow green icons. The only way to alter this new page is to "cancel" it. I have no idea what I did to deserve this, a goof up perhaps or is this something new?