Control panel … Folder settings .. File types
(translated from Danish .. not sure that terms are exatly like that in English)
You should set your preferred browser as the default application to open .html files. Sounds like it is only for .htm files as of now. If html-filetype is not registered with the system just add it! You might choose to set it for xml, .shtml and .xhtml and more as well
The setting is available from the settings menu of most browsers too.
Very strange that it is opened in Excel. You did not use the export as .CSV option this time? When M$-Office is installed it sets Excel as the default program for .csv-files!
BTW: thanks for your mail!