The developer behind the popular firmware umbrella tool, @notcom, has recently updated TinyUmbrella for Mac and Windows.
The new update (version 4.21.13) brings iOS 4.3 GM support as well as uses your system proxy settings when launching the TinyUmbrella loader.
For those not familiar with TinyUmbrella, it is a utility that allows you to save SHSH blobs, files that are necessary when you try to downgrade your iPhone to a previous iOS version that Apple is no longer signing. Without these SHSH blobs, you can not downgrade the iOS version. While you may not care about it right now, if you plan to jailbreak in the future it is highly recommended you save your iDevice’s SHSH blobs. These SHSH blobs may also come in handy for new jailbreaks, such as Jailbreak Monte.
To save your SHSH blobs, simply download TinyUmbrella from here, connect your iDevice via USB to your computer, launch TinyUmbrella, and click “Save SHSH” button.