This poorly named Firefox extension aims to fix those pesky 404 error messages by retrieving an older version of the Web site for view. However, we found this free add-on's performance hit-and-miss.
Using Wayback Machine's archiving capabilities, 404 Page is Not Found Now It Will Be purports to retrieve an older, archived version of the Web page you're trying to locate. The interface consists of an archive shortcut button that you have to drag and drop to your toolbar. You wont find a Help menu here. While testing, we never came across a Web site that automatically loaded the archived Web page. Instead, we had to click the Archive button each time we encountered a 404 error page. The results were unreliable. Sometimes an older, archived page would appear, but on several occasions the connection failed.
It's free, but 404 Page is Not Found Now It Will Be isn't very effective and won't help most users bypass the annoying error message that gives this tool its name.
If a page was (re)moved and now shows '404 page/file/site not found' error, this tiny extension uploads archived version of a page (from wayback machine at archive.org). If 404 error related message is not put in the HTML title tag of the missing page, this extension will not automatically look for an archive, but user can click on Archive button instead. Clicking on that button will show archived version of any page. False detection occurs when an existing page is about this error and has error message in HTML title tag. However, these pages are not common. When this happens, just click Cancel when confirm box appears, and that page will be added to whitelist and will not be mistaken again for missing page.