User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:73.0) Gecko/20100101 Firefox/73.0

Steps to reproduce:

Went to our Intranet running under HTTPS with Firefox developer on macOS and the page fails to load.

Actual results:

Page failed to load and console shows the error: "The character encoding of the HTML document was not declared. The document will render with garbled text in some browser configurations if the document contains characters from outside the US-ASCII range. The character encoding of the page must be declared in the document or in the transfer protocol."

Expected results:

Page should have loaded. Same Intranet page loads correctly in current release of Firefox 72.0.2 (64-bit). See screenshot for a comparison of page loading.

1. Your screenshot shows active add-ons. Can you reproduce the issue when starting with add-ons disabled (safe mode)?
2. If yes, please check if the issue is reproducible in the latest Nightly.
3. If yes, can you find the exact regression range?

I think you misread the screenshot. The browser failing is the developer edition showing no extensions running. Additionally it was started with no extensions running in safe mode. The screenshot shows the top browser working correctly (Firefox 72) and the bottom browser failing (Firefox 73) with no extensions running.

That doesn't address the other two points raised at comment 1. It's unlikely this report will advance without either that information or a publicly accessible link where the issue can be observed.

(In reply to Mark Bokil from comment #0)

Page failed to load and console shows the error: "The character encoding of the HTML document was not declared. The document will render with garbled text in some browser configurations if the document contains characters from outside the US-ASCII range. The character encoding of the page must be declared in the document or in the transfer protocol."

This error does not stop the page from loading further (potentially with garbage showing up in place of non-ASCII text). Something else is causing the page to show up blank.

This is very likely to be a regression of bug 1551276.

(In reply to Mark Bokil from comment #0)

Created attachment 9123690 [details]
Page failed to load and console shows the error: "The character encoding of the HTML document was not declared. The document will render with garbled text in some browser configurations if the document contains characters from outside the US-ASCII range. The character encoding of the page must be declared in the document or in the transfer protocol."

Firefox 72 should have also displayed this error. This message means that Firefox had to guess the text encoding. Firefox 73 changed the way of guessing.

As noted in comment 4, it's unlikely that this bug is really about the character encoding.

In any case, this bug isn't actionable without a test case to experiment with.

Please reopen once there is a test case.