Fix for Unable to comment on Youtube videos

On November 6, Google changed its YouTube property to only allow comments from Google Plus accounts.

So basically if you want to comment on YouTube videos you must have a Google Plus account; but even after having a valid Google plus account some users face issue that they can't comment on YouTube videos.

Symptoms:

1. You get the usual comment box that now says "Share your thoughts"

2. A window quickly appears that tries to load this URL: 'https://plus.google.com/u/0/wm/4/up/?type=st&client=7&gpsrc=gpfw0&parent=https%3A%2F%2Fapis.google.com&proxy=I1_1384465986211&rsz=1&hl=en_GB'

3. The window has a blank page and the window closes in about a second or two, i.e. nothing loads

4. Window closes and you get back to the same YouTube video page where it still says "Share your thoughts".

5. Even if you have turned YouTube safety off. Reseted chrome's browser settings, cleared all browser data except from 'Clear data from hosted apps' and 'De-authorise content licenses',  non of this resolves YouTube comment problem.

6. However YouTube comment problem does not exist when you use Firefox 23.0 or 25.0.

Solution:

Usually, the problem with that pop-op window is that you are disallowing certain 3rd party cookies, which are required in order to post with Google+.

To allow them with Chrome, go to Settings > Show advanced settings at the bottom > Content settings. Then, either 

1) un-check Block third-party cookies, or 

2) click Manage exceptionsunderneath it, and then paste "[*.]google.com" into the box and click Allow.

3) That's it refresh browser and now YouTube comment should work.

To allow them with Firefox, go to Tools > Options > Privacy tab. Then (assuming you have Use custom settings for history selected), either 

1) select From visited for Accept third-party cookies, or 

2) click Exceptions and then paste "google.com" into the box and click Allow.

3) refresh browser and check YouTube comment should work.

Some people have advised to also allow youtube.com, though this doesn't seem necessary for me.

Update:
You don't need to allow for the whole [*.]google.com

The only exception that you need to add is [*.]apis.google.com

So remove the [*.]google.com exceptionsand then just [*.]apis.google.com 

Why does this matter?
It is a h-ll of a lot less intrusive when it comes to privacy.

When you allow for [*.]google.com you bascially say "Allow third party cookies for all google sites (google.com initself andall the subdomains like plus.google.com, maps.google.com and so on).

Only using the apis subdomain means you open up to third party cookies just for that subdomain and nothing else!
Less third party cookies => More privacy!