From https://bugzilla.mozilla.org/show_bug.cgi?id=1577413#c2:

The Google C++ coding style encourages "short" functions at https://google.github.io/styleguide/cppguide.html#Write_Short_Functions, but does explicitly not mention a particular length. I would make this a bit stricter. A hard limit cannot be set, probably. But a soft limit of much less than 200 lines (maybe 40 lines?) would be good, encouraging the author/reviewer to seriously reconsider if something should be done about the length of the function in that case. I will create a bug to include a rule related to this in our style.