On this page https://developer.mozilla.org/en-US/docs/Mozilla/Projects/NSS/Reference/NSS_functions there are many links to the source code of functions via MXR. However these links lead to sites like this: https://mxr.mozilla.org/security/ident?i=NSS_GetClientAuthData Which says mxr is retired and something called DXR can be used. However that link only gives a 404. This causes lots of broken links on MDN.
The MXR stub page only provides a possible end point on DXR; they are not, and can not, be perfect. The correct solution is that pages on developer.mozilla.org (and elsewhere) should be updated to point to the correct place on DXR.