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.
But there is workaround.
Just copy dropbox link to your file. It may look like this:
`https://www.dropbox.com/s/fy44flf3pw2afsp/thefile.js?dl=0`
and then replace `www.dropbox.com` with `dl.dropboxusercontent.com`.
So the link should look like this:
`https://dl.dropboxusercontent.com/s/fy44flf3pw2afsp/thefile.js?dl=0`
Now you have direct link to your file and you can src it in your html.
P.S.
While I was writting it just realised I can write css/js inline...