Because LG has made some changes in its server settings, You can not use browser to download the firmware from above URl from LG server directly with Browser. Please check this guide on how to solve the blank page issue when trying to download LG firmwares.

To unbrick/Restore Your phone back to Stock, You need to download and install:

1) LG USB Drivers
2) LG Up Software
3) LG UP DLL file for your phone model