Taking a look at some of the “experimental” add-ons for Firefox, this one caught my eye.  ErrorZilla Plus looks like it is a refreshed version of the original ErrorZilla with a few more perks.

Here is a little more information from the developers…
This extension is a mod of the ErrorZilla Mod extension. I added a “Proxify” function into it. When error page shows, you can choose a web proxy from a list and browse the unreachable network address via it.  From [...]

Knowing that by the time I get there, the page will probably have already been dugg to death or viewed by so many people on reddit, del.icio.us and others that I won’t be able to view it, I often give up.  Firefox gives us a few more chances to bring that popular web site back up from the dead.
Handy Links and Bookmarklets
First solution I have to share with you would be the bookmarklet way of doing things.  Thanks to [...]

Traveling to a link you want to check out, only to find that you reach the dreaded 404 (file not found) is a pain in the browser. Let say you bookmark a link, think you might read it later and then when you finally get the time to a few months later the page is gone. Well if you have Firefox there is new 404 extension that could help you recover your lost page.
Getting an award for the [...]

Ever find yourself on a “Page Can Not Be Found” Web page? You are left with an empty feeling inside, because you do not know what else to try. For those of you who might run into error pages more times than the rest of us, you need ErrorZilla. This extension will give you a prettier error Web page, as well as some neat tools to help you find what it is you were looking for. [...]