New warning-as-error in Rust 1.43:

0:07.01 warning: unused doc comment
0:07.01 --> toolkit\components\bitsdownload\src\bits_interface\monitor.rs:143:5
0:07.01 |
0:07.01 143 | /// This method is essentially a error-handling wrapper around try_run.
0:07.01 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ rustdoc does not generate documentation for macros
0:07.01 |
0:07.01 = note: #[warn(unused_doc_comments)] on by default
0:07.01 = help: to document an item produced by a macro, the macro must produce the documentation as part of its expansion

Same at request.rs:687.

Apparently doc comments aren't meaningful on macros, and Rust 1.43 introduced a new lint for this.

https://hg.mozilla.org/mozilla-central/rev/5b74b50fc17e