Ublock: Element picker fails to load on dropbox.com

[yourduskquibbles]

Element picker tool fails to load entirely on the dropbox news site

Errors are also reported in the chrome console.

One or more specific URLs where the issue occurs

https://www.dropbox.com/news/company/announcing-the-dropbox-foundation

Screenshot in which the issue can be seen

Chrome Console log after trying to launch the element picker.

Specific error message in Chrome Console Sources

Steps for anyone to reproduce the issue

1. Go to https://www.dropbox.com/news/company/announcing-the-dropbox-foundation
2. Attempt to launch element picker tool
3. Observe no element picker tool launch and errors in console

Your settings

• OS/version: Windows 10 64-bit
• Browser/version: Tested on Chrome stable v64.0.3282.167 and Firefox v58.0.2 64-bit
• uBlock Origin version: 1.15.7.3 (chrome dev build) 1.15.11b0 (firefox dev build)

Your filter lists

Tested with uBO default filters on new test installation,

Your custom filters (if any)

NO custom filters or other extensions installed

[gorhill]

A more severe manifestation of the same issue reported in #2240: the site uses a content security policy directive sandbox, which prevents uBO from injecting its element picker iframe.

[uBlock-user]

Is it related to this Chromium bug ?

[gorhill]

Close but no. uBO injects an about:blank iframe into the page for element picking purpose, this is being denied because of the page's CSP -- webRequest is not involved in this case.

The Chromium issue you link to was also affecting uBO but has been resolved in the latest dev build, see #2823.

[uBlock-user]

Can't reproduce on Firefox or Chromium, is this still an issue ?

[gorhill]

The site changed its design, we need a new repro case.

[gorhill]

Since we lost ability to reproduce, I am going to close this issue. A new issue should be opened should there be a new case of element picker failing to inject -- especially given that the picker's injection mechanism has changed significantly lately.