In an upcoming patch that I am working on, I will be converting all tests that have a hardcoded ‘localhost’ to be ‘mochi.test’.
mochi.test will be defined in the PAC file (automatically generated in the profile: user.js), similar to how example.com is currently defined. By default it will proxy to 127.0.0.1 as it has in the past.
Once my patch lands, new tests won’t work if ‘localhost’ is hardcoded in there. Please keep this in mind while writing new tests!