Hey,
Just switched to Firefox and tried to find the way how I can replace the start page.
The only way I’ve found is use New Tab Override extension. It allows to set custom html I want to use for start page but other files like css/js and fonts should be linked.
I don’t have them anywhere except my Dropbox and of course usual dropbox link isn’t working since it opens Dropbox’s page where I can download the file itself.