Use findLogins() for efficiency

[aswan]

The current implementation was cribbed from the add-on sdk passwords module which uses getAllLogins() and then filters the results. For scenarios where a user has lots of stored login information, we can be a lot more efficient by using findLogins()

[bobsilverberg]

This has been addressed in the patch for [1]. I will mark this as fixed when that patch lands.

[1] https://bugzil.la/1324919