Error: Error downloading https://downloads.arduino.cc/packages/package_index.json

Any time I attempt to verify or upload code, I get the error "https://downloads.arduino.cc/packages/package_index.json". I've seen quite a few posts online about this issue, but none have solved my problem. I've tried:
-Accessing https://downloads.arduino.cc/packages/package_index.json in browser (worked)
-Taking down my firewall
-Removing package-index.json
-Removing the /arduino15 folder
-Uninstalling and reinstalling the IDE, including redownloading the installer

Does anyone have anything else to try? Is there a way to run code without accessing this file online?