One of the things I regularly do is to create a new branch of an existing web project, to work on a new feature. Thus, I might have sites example.com, dev.example.com, and many cases of branchname.dev.example.com. Across all sites, usernames and passwords are likely to be identical, since I’ll usually be using a recent-ish copy of the live database. However, all browsers will treat these sites separately, so even though my browser knows the password for user “mytest”, it won’t recall it on a new branch.
Plugin proposal to the rescue! I think it’d be useful if we could have a browser plugin that allows the user to add a regular expression specifying how (sub-)domains are to be treated as identical for password-remembering purposes. I don’t know whether browser security models will permit it, but it’s worth a try.