My program for Opera

Get File Size is an browser add-on that allows you to find out the size of a file before downloading it. Get File Size does not require any special skills, just right-click the link to a file and select Get File Size, the program will immediately show you the size of the file.
Moreover, Get File Size will show you the date when the file was last modified, file type, server response time and estimated download time. Get File Size can also retrieve the dimensions of JPG, GIF, PNG and BMP images without downloading the whole image.