This has probably happened to you: You've opened a dozen or so tabs in the background and then closed the page that linked to them when suddenly one of them flakes out and your train of thought is interrupted by an ugly pop-up error message. Worse still, the tab is now labelled "(Untitled)" and the URL you were trying to get to is long gone. This stupid behavior is fixed in Firefox 1.5, but if you're not running the beta you can get (almost) the same fix in your current version.

Here's what you do: Enter about:config into your address bar, right-click on the list that appears and choose New > Boolean. Enter the name "browser.xul.error_pages.enabled" and when the new option appears in the list double-click on it to set it to true. You might have to restart Firefox for this one to kick in, but when it does you'll be treated to descriptive error pages that don't pop up in your face or erase the URL you were trying to get to.