Decrypting SSL using Wireshark on Linux vs Windows

In Wireshark (Ubuntu 14.04) you can Right Click the SSL stream, and go to:

Protocol Preferences > Secure Sockets Layer Preferences

Here you can add RSA Key lists where you can enter the password of the private key used to protect the communications. You can also enter a Pre-shared Key or a Pre-Master Secret log file (which I believe is what you have).

Here's a tutorial on how to decrypt SSL traffic with Wireshark in Linux.

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As an alternative I would look into using a proxy like Charles to act as a man in the middle to view SSL traffic between websites. It makes it very easy to see the decrypted traffic, and you can have multiple sessions going at once. This is ideal in a closed off network since you'll have to install their CA into your trusted store.

But this is a great way for debugging/viewing secure web traffic.