Top level coordinates are being returned when calling window.mozInnerScreenX and window.mozInnerScreenY even inside OOP frames. Instead, I think those values should refer to the coordinates of the inner OOP frames.

This API seems like something we should be removing from the Web. For internal use, it also doesn't seem like a great API in the face of transforms.

(In reply to Jonathan Watt [:jwatt] from comment #1)

This API seems like something we should be removing from the Web. For internal use, it also doesn't seem like a great API in the face of transforms.

WONTFIX because content process should not be allowed to know its screen coordinates. Parent process can map content process's document-relative coordinates to screen coordinates.

WONTFIX because content process should not be allowed to know its screen coordinates. Parent process can map content process's document-relative coordinates to screen coordinates.

Since these are in a publicly documented api, ( https://developer.mozilla.org/en-US/docs/Web/API/Window/mozInnerScreenX ), I think there is more to do here. Some websites might be using these. Either we deprecate or remove the properties and their corresponding documentation.

(In reply to Neil Deakin from comment #3)

Since these are in a publicly documented api, ( https://developer.mozilla.org/en-US/docs/Web/API/Window/mozInnerScreenX ), I think there is more to do here. Some websites might be using these. Either we deprecate or remove the properties and their corresponding documentation.

In that case, I'll reopen this bug. WONTFIX'ing this bug for Fission means some websites using mozInnerScreenX or mozInnerScreenY may be broken.

Some options to address this bug:

• Do nothing. If anyone reports a broken website, we can then reach out to the website or decide to actually fix this bug. What should web developers use instead of mozInnerScreenX or mozInnerScreenY?
• Remove mozInnerScreenX and mozInnerScreenY. Websites accessing these properties will get undefined values. Performing any math with undefined will produce NaN coordinates.
• Hard code mozInnerScreenX and mozInnerScreenY to return 0 or window.screenX and screenY.

Here is a proposal for standardizing innerScreenX and innerScreenY: https://github.com/w3c/csswg-drafts/issues/809. The use case given in the proposal is mapping screen coordinates from an eye-tracking device to a document-relative position on the web page.

Note that now bug 1550800 landed, mozInnerScreen{X,Y} works properly in OOP iframes with transforms.