404 Error Page Status

Feature Description

We want Firefox to override server-supplied 404 error pages in certain cases.  The Firefox 404 page should provide the user with tools we think are more useful to the user for resolving the situation, than the server supplied page.  This includes alternate ("did you mean") URLs derived from the Places database and some pre-loaded search links/controls.


The newest patch is almost ready for review.

This patch is mostly focused on making the code right, but there are a couple of functional changes:
  • The Firefox 404 error page is now pref-controlled.  There's a pref to turn it on and off, and a pref to limit which server-supplied 404 pages we'll override.  Currently we will only override server 404 pages of 512 bytes or less.
  • We're dropping the background image for now.

Next Steps

  • Complete the patch and get it in for review.
  • Blog about it.


  • This feature is being tracked by Bug 482874 - Provide a friendlier/more useful alternative when the user encounters a 404 error page.

Edit: Added Notes section.

7 responses
Can you provide us with the bug number, so that we can follow the progress, and more specifically I can update my themes for it (if needed)?

Thanks, Alfred

Didn't IE get attacked quiet savagely for this behaviour? Or do you think you can do it "better"?

(of course it's always different if there is an "off switch" - as long as this doesn't encourage web devs to start returning 404 pages without a 404 HTTP status... my my what a mess that would be...)

If the default is overriding everything below 512 bytes, we're driving web designers to make their 404 pages a bit heavier to not be overridden, but it could be worse, I guess...

As Alfred said, never ever reference to work you're doing in the Mozilla community without specifying the bug number, people will always hunt you down for it ;-)


I have been stewing over this bug.. namely the URL bar likes to not stay in focus... Like when you type in a URL that is not correct and it does not load.. the error thing will kill what you are typing in the URL bar.


How about showing both? Side-by-side or one above the other.
This is Bug 482874 - Provide a friendlier/more useful alternative when the user encounters a 404 error page. I updated the blog post as well.
I'd rather see an error "bar" like the "do you want to save this password" or the "Firefox prevented this page from automatically reloading" with the button "Help me fix this" or something.

I know I've put in some bogus code in my 404 pages so that Internet Explorer won't show their error page instead of mine.