1476439 - CSP blocks adding a new CSS rule from the Rules Inspector

Status: RESOLVED DUPLICATE of bug 1228985

(DevTools :: Inspector: Rules, enhancement, P3)

Description

[Matthew N. [:MattN]]

Similar to bug 1391994, but filing separately in case that solution doesn't address this use case (or in case we want to just have better error handling in the short term rather than making it work), if I click the + button on the Rule pane of the inspector, I get a CSP error in the console but that's not obvious.
> Content Security Policy: The page’s settings blocked the loading of a resource at self…
as it tries to append a new stylesheet.

Some options:
* Show a menu with a list of stylesheets to choose an existing one to add to
* Give feedback about why the button doesn't work… maybe disable it in advance and have a tooltip mentioning CSP?
* Always append the rule to the last existing stylesheet in this case?
* Badge the console tab so I know to look there for new messages
** Internet Explorer had this for page errors a long long time ago.