When I view the PDF file in a browser such as FireFox without downloading the file into my PC, does FireFox temporarily store the PDF file in my PC?

I heard that FireFox has been sandbox heavily and there is no need to worry about malicious PDF file downloading to PC, is this true?

What about previewing the PDF file in browser but in gmail and google drive? Is there any difference between browser PDF viewer and PDF Preview feature in Gmail/Google drive/One Drive?


1 Answer 1


The browser is not just a window to the Internet you can look out through. What ever you see in your browser must first be downloaded into your computer in order to render it on your screen – whether it is stored in the memory or on the file system.

It does not matter that much whether a file is saved on a drive or not. The malicious PDF document cannot run code while it is resting on a disk. Instead, malicious (PDF) files use vulnerabilities in the applications reading and rendering them. Here, the sandboxing on a browser helps, because there is one extra layer of protection: even if a malicious document or page is able to run arbitrary code inside the sandbox, there must simultaneously be another vulnerability that allows it to escape the sandbox.

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