This has nothing to do with needing to "clean" the "system" (i.e. Windows installation). I'm not using Windows and I'm getting the same prompt to save three aspx files on each view. Though - perhaps due to a difference in the Firefox version, or a difference in the Linux version of Firefox - there's not one message, but instead three file saving dialogs pop up. And when all of these are canceled, the page can be used as usual.
aspx files are for ASP.NET scripting, used by Microsoft-based web servers. I have no experience of ASP.NET or Microsoft server software, and so do not know what the most likely error is. In any case, something is broken. Perhaps some configuration is wrong, or perhaps some files have been corrupted. As a result the files do not run as they should, and instead garbage (harmless but annoying) is sent to the browser. The 3 downloads are all blank, by the way - empty files.