Mega Now Works in Firefox with Official Add-on, Bypasses JavaScript File Writing Limitations

One of Mega's distinguishing characteristics is that, until now, it's been web-only. In fact, it's been Chrome-only, the site only works properly in Google's browser. Mega explained that some of the more advanced web technologies it uses aren't supported or don't work that well in other browsers.

Now though, Firefox users are getting some support in the form of an official add-on. The add-on is offered on the site itself to any logged-in user running Firefox.

Users get a prompt encouraging them to install the extension to get the most out of the site. The extension doesn't do much after it's installed, there's no UI or anything.

But it will allow users to download files of any size and grab several of them at a time, useful if you need several of your big files and fast.

The add-on completely bypasses Firefox's download process, it even saves files in the default Downloads folder rather than whatever you have set in the browser.

It has to do this because Firefox doesn't support writing files from JavaScript. Mega needs this since the files stored in the cloud are encrypted and can only be decrypted locally.

In Chrome, Mega downloads the file you need, the encrypted version, decrypts it locally and provides you with the original version.

Since the encryption/decryption method is implemented entirely in JavaScript, the site needs to be able to alter local files using JavaScript.

The only other browser to offer JavaScript file writing is Internet Explorer 10. However, it only allows this for files stored in RAM, not for files on the disk.

This means that the encrypted file has to be "downloaded" into RAM and then decrypted there as well. Memory usage peaks at twice the file size, so a large file would quickly use up quite a lot of RAM, a DVD image would need more than 8 GB of RAM for example.

Firefox, Safari and Opera have no JavaScript file writing whatsoever. The Firefox add-on solves this problem by handling the download itself. It saves the encrypted file locally first and then decrypts it when the transfer is finished. All of this happens behind the scenes of course, all you see is the final, decrypted file.

Note though that you can use Mega without the extension, downloads will just be slower and you will only be able to download one file at a time.