IE9-10 throws on elements created in popups (see #14150), FF meanwhile throws
on frame elements through "defaultView.getComputedStyle" (see #15098)
Use "defaultView" if in the popup which would fix IE issue,
use "window.getComputedStyle" which would fix FF issue.
And everybody wins, except performance, but who cares right?
Fixes#15098
Closes gh-1583