edp.pt still recognizes login after wiping all cookies in private window, but Firefox's own deletions works

[TiagoTiago]

At first it freaked me out thinking they had some sort of insane tracking system that they were using for sustaining the login even after wiping all the Private context cookies and site local data; I even tried switching to different IP. But it turns out it seems there is something this extension isn't covering that this site uses, I'm not sure what. But clicking on the padlock icon in the URL bar and telling Firefox directly to "Clear cookies and site data" does work, so it seems it might be something this extension isn't covering.

Unfortunately, I suspect it's gonna be kinda tricky to debug with this site as it is one of the electricity companies in Portugal; I'm not sure you can create account without having a physical address hooked up (or available to be hooked up) to their system, or even if you can create a login without hiring them. Probably a more promising first area to investigate would be comparing what Firefox's functionality does versus what this extension touches.