New update Pangu8 untether 0.4 is available on Cydia now. It fixed the memory issue that caused many apps such as MobileSafari crash on 32bit devices. If you have problems with such situation, you can fix with untether 0.4. Don't forget - Jailbreak 8.1 iOS is free.
Complete guide "How to Jailbreak 8.1"
If you want make Untethered iOS 8 jailbreak 8.1, ensure that you have, and complete, the following as all are necessary to ensure the success of an untethered jailbreak on Apple’s latest public firmware. If you want download iOS 8.1, you can do it from here.
Any of the above iDevices running iOS 8 through 8.1 that were not updated through the Setting app’s OTA (over-the-air) update option.
If you performed an OTA update, follow the below prerequisite instructions.
Also, ensure that your device does not have a passcode set or Find my iPhone enabled, both of which can be set back post jailbreak – this is very important.
Windows-based PC is officially supported Pangu8 (last version you can see here) should update their utility soon. For the time being, either create a Windows partition using Boot Camp Assistant or setup a virtual machine.
The Latest version of iTunes 12, as well as the all-new Pangu Windows jailbreak iOS 8.1 utility, both of which can be found, and downloaded, from the download section below.