Are the signing extensions only for web apps? What about phone apps? Does the phone app store your private key locally and sign things, acting like a signing extension?
Discussion
The extensions like Alby and Nos2x are just for web apps.
What's available for mobile apps depends on your operating system. There aren't currently any signer apps available for iOS. On Android we have #Amber, though, and it's fantastic!
It can be a challenge to figure out which apps actually work with a signer app, though. Here's my wiki article with as complete a list as I have been able to compile:
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