How to stop web page refresh to view disappearing error message

We're working on a Joomla site for GiveCamp, and our code is running into some error in production that didn't occur in test.

Nothing is showing up in the server logs, and some error appears on the screen very very briefly, then is replaced by another error page.

How can we freeze the display to view the first page?

Like stepping through code in a debugger, but in the browser?

The only thing we've come up with is making a video and stopping the playback; there's got to be a smarter way of capturing the web traffic, right?

We're open to using a different browser or adding extensions -- I think we've viewed this in Firefox and Conkeror, so far...

UPDATE: we ended up recording a screen-case, then stopping the playback to see the error. I am still hoping to find a better solution, something that would be caching the web stream.

I know it might be late since you've already found your solution, but the following might be useful for for anyone else having the same problem:

Try using a FF extension to capture the response headers like httpfox or live http headers. These will allow you to capture everything received from the web-server and then go through it to find your message. There are also a bunch of dedicated packet sniffing tools such as wireshark - this will capture everything. If you're on windows, theres an awesome app called fiddler.