Why this strange behavior in google chrome and IE?

I am using fpdf library and generating pdfs... What happens when i click ExportToPdf button in firefox it opens the Save as dialogbox but google chrome and IE just opens the pdf file in browser, 开发者_JAVA技巧the save as doesn't seem to open it... Why this strange behavior?

Use the content-disposition response header to control this behaviour - if value is inline then pdf will open inside the browser, attachment will show save as dialog box.