Comment 74 for bug 52667

Re Comment #70:
> - provide a scriptable interface for arbitrary header/value pair requests (no
bug yet, afaik)

Aah, that's exactly what's needed! It seems crazy to be sending this stuff through the UI just because an extension needs it.
When I was trying to look at implementing this bug, I eventually gave up because I couldn't work out how to do that...
There are plenty of comments on Bug 236954 that indicate this too. Maybe we should file a new bug?