This change was meant to lower the usage of CORS proxies and improve loading time, so that HTML documents from https://raw.githubusercontent.com could be fetched directly. I didn't realize that HTMLPreview is used outside of GitHub/Bitbucket, like with Dropbox. I will make an exception for such cases.

Ah, I understand.

Yes, a friend of mine uses the page with dropbox (https://jdelcastilloshideout.blogspot.com/2020/09/paravicini-y-la-roca-rodante.html) and asked me why the page stopped working, so I investigated and found the issue.

Thanks for the quick reply 😊. An exception is enough for my friend.

Sorry for the reply, but perhaps you have disabled notifications of pull requests.
I investigated the issue and found a solution that also should drastically reduce the number of petitions to the cors proxies. More info in the pull request: #96

You can check the result here:
https://trianguloy.github.io/htmlpreview.github.com/?https://www.dropbox.com/s/mgw65rktedx4pjl/Hello%32world.html?raw=1
https://trianguloy.github.io/htmlpreview.github.com/?https://github.com/twbs/bootstrap/gh-pages/2.3.2/index.html
https://trianguloy.github.io/htmlpreview.github.com/?https://github.com/documentcloud/backbone/blob/master/examples/todos/index.html

I also started encountering this error, but my file is on Github. Here's the file:

https://github.com/openmm/pdbfixer/blob/master/Manual.html

The following link produces the error message given above:

https://htmlpreview.github.io/?https://github.com/openmm/pdbfixer/blob/master/Manual.html

Is there anything I can do to work around this problem?

@peastman The link you posted above (https://htmlpreview.github.io/?https://github.com/openmm/pdbfixer/blob/master/Manual.html) works fine for me. I checked the mentioned issue from your repo and the link is different. Simply update the link to this one and it will work again.