If is not a fullscreen mode as you expect it, but similar. ( and as stated in other comments it is not recommended, due to a lot of space left if you are on a larger screen. Size of objects won't change, just screen size)
You can go to folder "1" and open find start.hta.
Open it with any editor and on the line 7 (line number might change) there should be 'maximizeButton="no"'. If you change its value to 'yes' then on the next start on the top right corner you will have maximize button.
If is not a fullscreen mode as you expect it, but similar. ( and as stated in other comments it is not recommended, due to a lot of space left if you are on a larger screen. Size of objects won't change, just screen size)
You can go to folder "1" and open find start.hta.
Open it with any editor and on the line 7 (line number might change) there should be 'maximizeButton="no"'. If you change its value to 'yes' then on the next start on the top right corner you will have maximize button.