FAQ:I can't download from the user repos, all files are saved as HTML
This is a problem with your web browser (probably Internet Explorer or Edge), which makes assumptions about file extensions.
The quick fix is to use a different web browser (Chrome and Firefox are known to not show this bug). With these browsers, things will most likely save automatically in the correct way. If not, at least chrome has a checkbox in the save-as dialog to force the correct extension.
More ideal solution
Alternatively, there is a more ideal solution: Install the plugin for downloading assets from within makehuman instead.
You can find the asset downloader plugin as well as installation instructions at https://github.com/makehumancommunity/community-plugins-assetdownload