Bytingshark - user.js who will try show to you currently playing songs file size. Works on all modern browsers like Firefox, Google Chrome, Opera and (maybe) Safari.

P.S. I haven't tested newest version (2012.10.23) in all modern browsers. And some act strange for no apparent reason (Opera). May come back to it, some other day.

Install

Firefox

You will need to install Greasemonkey add-on. After that just open bytingshark.user.js and install it.

Google Chrome

Open Tools > Extensions and enable 'Developer mode'. Then use 'Load unpacked extension...'.

Opera

Copy bytingshark.user.js script into User JavaScript folder. If you don't know where yours located at (or haven't added it yet):

1. Goto Preferences > Advanced > Content > JavaScript Options ...
2. There will be field named "User JavaScript folder", set it where you putted bytingshark.user.js script.

Safari (might work, too lazy for test)

How to run Greasemonkey scripts in Safari