Debug Pound Varnish Apache - ajax

I have a server configured with Apache and Varnish, we are using Pound to handle port 443.
Everything runs smoothly and the site speed is amazing.
I have one little bug, when clicking on an AJAX button, sometimes the request hangs for 60 seconds before posting.
I am trying to figure out where the bottleneck is and what's holding things up.
What "listener" or "debugger" can I use to trace exactly what happens on the server when I click on that AJAX button on the front end.
Beginner question, so if I'm missing the obvious please let me know

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Using a third party Windows Application, Fiddler Classic's proxy changes, "click to reenable" capturing. Are any requests getting by unnoticed?

I recently began using Fiddler to capture requests from a windows application that I believe is sending malevolent requests. This said application actually has a browser extension for both Chrome and Microsoft Edge. However, only on the Windows Application does Fiddler gives me a yellow pop up: "The System proxy was changed, click to reenable Fiddler capture." This happens specifically when the App begins running and the user logs in.
An example is seen on here: Fiddler not capturing traffic. Proxy settings keep getting changed
I also notice in my windows machine network proxy settings that the App automatically checks "use a setup script" and provides a link to their proxy script.
On my machine, I clearly still am seeing many requests after clicking the yellow pop up. I also am still seeing many requests called by this App. However, I am worried that there could be an instance where the App is clearly able to send requests that it can hide from Fiddler, and only let Fiddler see the requests it wants it to.
The reason I believe this is that Fiddler is a proxy, and the App is yet another proxy. Fiddler doesn't know that it's intercepting a network's traffic through the App's proxy. So Fiddler wouldn't know if it's not hearing everything, and neither would I.
Is this a realistic fear?
If so, where can I find some more information on what is happening, and how to bypass it?
If not, that's all I need to know.

Fiddler on Windows 10: All Captured HTTPS Traffic Dies

I've had a problem with Fiddler ever since my machine was upgraded from Windows 7 to Windows 10. If I configure Fiddler to decrypt HTTPS traffic, any traffic it captures is, for lack of a better word, killed.
For example, if I visit the (HTTPS) page that documents configuring HTTPS decryption, without Fiddler, I see it as normal:
However, once I begin capturing traffic, and reload the page, I get this:
All of the responses feature this same exception message:
I only use Fiddler occasionally, when I need to see what's going into and out of my apps. I could've sworn I was able to do this with HTTPS before migrating to Windows 10. I'm not sure what changed, but Fiddler has become fairly useless to me now that all the traffic it captures fails. Any help would be appreciated.

First HTTPS connection is very slow in Internet Explorer 11, what can it be?

When using Internet Explorer 11 to connect to a HTTPS site of my company, the first connection is very, very slow. Usually more than 30 seconds. After this first connection, I can browse the site with no problem. The problem just happens in Internet Explorer, it works fine in Chrome and Firefox.
If after the first visit, I clear the cache and cookies, the next page load is quick. I have to close the browser and reopen it to reproduce the problem. Even if I let the browser idle for a couple of hours, the next visit is still quick. The problem is just in the first visit of a browser to this site.
Below you can see the network view of the developer toolbar:
The first connection is a HTTP connection that redirects to a HTTPS connection. This connection is very slow. The two following connections are quick. If I close my browser and visit directly the third URL via HTTPS, it will also load slowly.
Here is the Timing in the Detail view (sorry, I can't change my company browser language to English):
What can it be? How do I debug it? With this problem, it is very hard to execute automated web tests.
I've had the same problem as well. It happens only when the HTTPS site is being accessed on a machine without internet access and only using IE.
A workaround that i've applied on LAN would be to update IE settings as described below:
Go to IE Options, advanced tab then locate security category and uncheck
“Check for publisher’s certificate revocation” and “Check for server certificate revocation”.
I've only found that workaround after seeing this post, so thanks for sharing :)
Since the problem happens only with HTTPS (right?) I guess that IE tries to check the revocation status of the site on the first visit. It probably caches the result, but only for the current browser session. There might be problems to reach the server responsible for the revocation (see OCSP/CRL settings inside the certificate) and thus the connection might time out. Chrome does not check revocation in most cases and Firefox might use a shorter timeout and ignore failures. You should see the attempts to get OCSP/CRL if you do a packet capture.

AJAX request from Internet Explorer 11 to a nodejs server running behind Apache proxy aborts randomly

On a page that uses angular, after a user action, a get request is made to the server to get some json data. Sometimes the request fails on Internet Explorer 11 (I have not tested on other versions yet). It works on Firefox without any issue. This request failure seems to happen randomly and I cannot put a finger on the cause. Here is the screen shot of aborted request:
Server Side
This particular api runs on nodejs but the request is proxied through Apache for this particular domain with following config settings
...
ProxyPass / http://localhost:8000/
ProxyPassReverse / http://localhost:8000/
...
Also, KeepAlive is on and KeepAliveTimeOut is 3 seconds (it was off before and i had the same problem)
What may be the cause?
When I took the apache out of the equation so that the requests are made to nodejs server directly, problem seems to have gone away. I suppose I am doing something wrong with using apache as proxy server(however, it seems to work on firefox/chrome without problems).
I would still appreciate a response about how to make it work with apache as proxy.
Update:
Now, I am running nginx as reverse proxy and all is fine. No such aborts.

Detecting when Firefox is showing a Server not found message

I'm using Firefox for a digital signage application, and there a couple of scenarios where a Server not found might result.
Network outage on boot
DNS fails to resolve for the homepage
Server (its homepage) fails to respond
Boots and the network just isn't ready by the time Firefox is loaded
Browser crashes, process is restarted, but the network is down
In such cases I would like to detect this state and simply kill and restart the process after a minute. Any other tweaks or suggestions, I'm all ears.
You do not need to consider the case whereby the loaded Web application loses Internet connectivity. That scenario I think has been handled by the Web app itself, once it has loaded.
I don't want to go down the local httpd or local extension/addon route.
Thank you in advance,
I've discovered a simple solution of overriding Firefox netError.xhtml to do a simple location.reload every ten seconds.
Source code can be found from https://github.com/Webconverger/iceweasel-webconverger/blob/master/content/netError.xhtml#L410

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