Why do I often have to refresh pages I navigate to once for them (or content in them) to load?

Question

I have noticed a bizarre pattern when using my PC, that when I open a link to a website, it often will often take a very long time to load, or time out. Sometimes content on the website will be drawn, but again, it seems to get "stuck" for an unusual amount of time before finishing. Most affected is Youtube; almost every time I navigate to a youtube video from another website such as Google, the video will not begin playing, but will instead just display the player controls with a black screen where the video should be and the buffering symbol, usually before displaying an error such as "The video failed to load".

The unusual part of this problem is that whenever this happens, refreshing the page always causes it to load almost immediately the second time around, without any problems. Note that I'm not talking about how some browsers will dump whatever has been cached to the "pallet" briefly when the page is refreshed or loading stopped; but that the second time loading the website being faster.

I have done my best to rule out some of the obvious causes:

My Windows 7 desktop computer is the only device that seems to be affected. I use Firefox on it (latest version, flash updated, etc).

My connection has more than enough bandwidth (30 megabits down, 4 up), and I've even tried QoSing all other devices to make sure this isn't happening due to usage spikes.

Wireshark is not showing any clearly unusual network activity (i.e frequently dropped packets).

Answer 1

If you have any add-ons, disable them all and try again. If that solves the problem, then it's obvious where to look :)

Also try safe-mode for your browser.