User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:68.0) Gecko/20100101 Firefox/68.0
Steps to reproduce:
- Open HTML file test.html attached to this report in Firefox in Windows, with attached test.css file in current folder.
- Using the toolbar, open Web Developer > Web Console.
A difficult-to-understand error or warning message appears, starting "Stylesheets without CSSOM changes..."
This message may be meaningful, but it includes several terms that are not in common use by programmers who wish to use the Firefox Web Console (including myself, a retired software engineer with 40 years of experience).
The message only appears once for this test case, and all my other pages. It disappears on reloading the page. There is no explanation for its disappearance.
I also do not know if this bug report also applies to the Browser Console.
Since my test case uses standard HTML5 and standard CSS, and furthermore uses only the CSP (security) standard method of including a separate CSS file, not "inline" CSS, I can see no reason why the program should appear to contain a problem of any kind.
Note that this error has been happening for a very long time, but I am finally moved to report it. I do not see exactly the same error report in Bugzilla, but it certainly is possible that this is a duplicate bug. I do see many related bugs, most still Open, so I imagine this issue may need to be elevated to a more urgent status level.
Note: in my own programming I attempt to use "strict" code that does not create any error messages in validators or other developer tools. I do understand (very well) that much modern software (such as programming frameworks) use loose CSS (sometimes for valid reasons of browser compatibility) that does generate CSS errors, however, I try to avoid this practice in my programming so that I can see my own CSS errors when I test, and at other times as well. The message described in this report certainly looks like a real error, and cannot be understood due to its use of unfamiliar terminology, with not even a link to an explanation.