Offline manual download as of 2017-10-09
Short description of error
Offline copy of manual contains external links for js and css files that should get copied into the download tarball.
Exact steps for others to reproduce the error
External URL's in the offline manual include mathjax js files linked from a cdnjs.cloudflare.com url and a css linked from fonts.googleapis.com
While it appears that every page links to the mathjax js files, I'm not 100% sure they are needed to read the manual or where mathjax is actually used, but if they are to stay in use they should get copied into the download tarball. Maybe only a section of the js and css needs to be copied to a local file.
There are several external links that cannot be included, for example youtube and vimeo links and the blender.org url. These should not cause issues reading pages and just show as broken links.