I also only use private browsing mode, but the login annoyance is not enough to make me use an app. Most apps in fact track like crazy (potentially even third-party apps for sites like HN), and the whole point of private browsing is to not be tracked.

Instead I just lurk most of the time since I'm too lazy to log in, which means I'm not really contributing with votes. Maybe what we need to do is reduce the friction in logging in. I've always turned off the browser's password saving features and use my own password manager; maybe I should reconsider that policy.

[edit] Nevermind, apparently Firefox can't remember passwords when in permanent private browsing mode. So much for that idea :/