Bypassing L1 encryption (highest level) is a well guarded "secret" and almost impossible to bypass, since the license keys are exchanged with approved hardware, and not software decoded like that extension you're talking about used to do. L3 usually have the low quality options of streams.

RedFox anystream I'm pretty sure is for L3 (anyone can correct me if I'm wrong), It's not free, and personally have not tested it so I can't vouch for how well it works, but I'm pretty sure you won't get 1080p (even though it says so, that's usually behind L1) or 4K from this. However you can give it a try with the free 21-day trial version limited to 10 downloads, and see if that's something you would be willing to pay for.

Does the "Widevine-l3-decryptor" extension not work anymore? I know that was a big deal when it came out

It is possible to decrypt L3 by dumping keys from an android device. Several guides and tools can be found here: https://cdm-project.com/How-To.

I have done this successfully in the past, but it is far from easy.

As an alternative for using an Android device with some hacking tools, you can use https://getwvkeys.cc/, but you need to sign up and get accepted.

This still works for me: https://github.com/medvm/widevine_keys

Only thing is you need a valid, non blocked CDM. But if you have a rooted android device you can dump that with: https://github.com/wvdumper/dumper