There is a bug with the autorefresh, which ultimately results in the browser refreshing the backpack continuously, refreshing the page as soon as the previous one finished loading. This isn't immediate, it takes some time to build up.

Steps to reproduce : (only tested on firefox 15, ffx 10 ESR & ffx 3)

• Open a backpack on tf2b
  
• go to "menu"; click "Disable Autorefresh"
  
• Open another backpack (or just F5 the current one)
  
• Wait one to two hours...
  
• More seriously : open firefox's web console (tools => Web developer => Web Console and watch the timestamps on the ajax calls. You'll get one after 10 minutes. But 10 minutes later ? 2 loads of the stripped page. 10 more minutes and that will be 4 calls.
  
• An hour after your last manual page load that will be 32 refreshes in a row. Which is enough that you may notice it. After 2 hours, your browser will most probably be continuously refreshing the page because it can't finish its refresh spree in 10 minutes.
  
• optional : getting tf2b to behave sanely again on your browser will require you to clean the cookie associated with tf2b.com called "norefresh". In firefox that's Edit => Preferences => Privacy tab => remove specific cookies => filter for tf2b => delete the one called "norefresh"

source of the problem : forgotten parentheses in tf2b.js :
related to
i.e. : Disabling autorefresh once sets the norefresh cookie, and if that cookie is set then register a new update timer each time init() is called. And init() is called at the end of each successful refresh in pageUpdate().
IOW : a basic time-bomb with exponential growth.

note that if you click "Disable Autorefresh" before the first refresh, it will correctly clear the timer, thus the website is usable if you can remember to always disable autorefresh after each bp load.

If you forget ?

Consequences will vary. On my eeepc the CPU drain of loading a bunch of webpages is very sensible (I pretty much stopped using tf2b before I put my debugging cap on and figured out this thing). On the pc I use to play tf I would notice sudden lag spikes of a few seconds (getting longer and longer until I figured I had forgotten to disable autorefresh in a tf2b tab somewhere). A friend I asked for troubleshooting help had pings to tf2b.com so high (250ms+) the only thing he would notice was the news line changing every second. The final nail in the coffin is a memory leak (closure scopes chains) caused by this mad refresh timer setting; leading to ever increasing browser memory. If I'd forget such a tab in a browser when going to bed, I'd come back to a crashed browser and most other processes heavily swapped.

Thanks for your attention, the otherwise stellar website, and thanks in advance for fixing this.