Well, it might be a coincidence, but it also wouldn't surprise me if it wasn't. Your identity was probably linked using fingerprinting. Private browsing mode offers almost zero protection against this. Even Tor isn't protected unless you enable the Safest security level (= completely disable JavaScript). This might even be done through multiple levels of indirection (mobile browser fingerprint -> Google account -> desktop browser fingerprint).
uBlock Origin is specifically one of the whitelisted extensions, and you can disable this feature by setting extensions.quarantinedDomains.enabled to false (in about:config)
Well, if you consider the accompanying HTML as well as a user mindlessly clicking orange squares as part of the execution, then yes, it is: https://jsfiddle.net/Camilo/eQyBa/
Well, I use Stylus, and it works fine on Android (but you need to use a "custom addon collection" to add it, which is only available on Beta and Nightly). I see no reason why Stylish wouldn't also work.