Mixed Content discoverability proposal

[Larissa Co]

Email #3: On the discoverability of Mixed Content permissions. Again, 
let's narrow the scope of this thread to purely discoverability issues 
for now, please! (We're discussing other interaction improvements right now)

You can find the overview of the proposal on pg. 12 of 
http://people.mozilla.com/~lco/Permissions%20UI/130806%20design%20patterns-permissions%20UI.pdf

The issue with Mixed Content discoverability is a bit simpler:

1. Most sites work fine when mixed content is blocked. We want to make 
the icon as inobtrusive to the user as possible in this case, but give 
him a tiny hint for where he can allow mixed content if necessary
- Have the icon animate in (e.g. "flash") on page load to call some 
attention
- Use a Neutral icon once the animation is finished

2. There are certain cases in which we know Mixed Content is likely to 
"break" the page (e.g. insecure CSS). Here, we want to give the user a 
stronger clue to where he can allow mixed content
- Have the icon animate in (e.g. "flash") on page load
- Have the doorhanger animate in on page load and then disappear 
automatically after a few seconds
- We need to discuss the proper heuristic for this case. Perhaps we have 
a whitelist of common sites? Maybe if the user visits the site the first 
time, he always gets a disappearing doorhanger? Maybe it's after a few 
site reloads? Maybe we detect which content is broken and we show it 
only for certain content types?

Again, once we've been able to discuss this proposal, I'll file the 
necessary bugs.

Thanks,
Larissa