STR: 1. Open DevTools' Inspector 2. On most pages, e.g. https://www.google.de/?gws_rd=ssl or https://www.mozilla.org/en-US/ the "Add new rule" button does not work ER: A new CSS rule can be added AR: An empty <style type="text/css"></style> is added just above the closing </html> tag. It's like this on most pages. On some pages (I could not see a real pattern here) it works, e.g. on about:home
I tested with both of the URLs provided in step 2, with Firefox 57, on Windows 10, and it worked fine for me. The new CSS rule is added in the rule-view, with a default selector, in edit mode (the <style></style> node is also added at the end of the <body>, as you said, which is expected). When this doesn't work, can you please provide a screenshot of the rule-view? Also, if you open the browser console (ctrl+shift+J) when it happens, is there any errors in there that could be helpful to us?
Hmm, can't reproduce either now. Probably fixed by something else in the meantime. Closing.
Status: NEW → RESOLVED
Last Resolved: a year ago
Resolution: --- → INVALID
You may have hit bug 1228985.
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