After setting the fission.autostart preference to true (so that cross-origin iframes will be out of process) and visiting a page with cross-origin iframes, the iframes go blank when the omniscient browser toolbox is opened.

With some more testing, this happens when using the regular browser toolbox (devtools.browsertoolbox.fission == false). It does not happen when using the regular devtools for the tab, however.

The problem here only seems to happen when initially loading the browser toolbox. Some more notes:

• Scripts in the iframe continue to run after it goes blank (e.g. dump statements are printed to the terminal).

• If the tab containing the iframe is loaded after the OBT is opened, the iframe looks and runs normally. With the changes in bug 1586359, the sources for the iframe's process can be inspected in the OBT, and breakpoints work as expected.

I am also seeing cases where the iframe can go blank when dragging around the browser window, even when devtools are closed. This problem might not be a devtools issue.

Confirmed this is not a DevTools issue.

Steps (on macOS):

• Open Firefox Nightly (with fission.autostart set to true)
• Go to https://codepen.io/sfi0zy/pen/XWWKqWZ
• Move the browser window around (I was dragging it by the tabbar)

==> The iframe goes blank

• resize the browser window

==> The iframe's content appears again

Duplicate of bug 1565786?

Yeah, I believe this is a dup of bug 1565786. (and bug 1562562).

Based on Bug 1586519 Comment 7, mark this duplicated.