June 16, 2008

Firefox extensions to bring back the dead

Author: Shashank Sharma

Don't you find it irritating when a Web page you bookmarked or favorited returns a 404 error on a subsequent visit? Or when a Web site is temporarily down? Firefox extensions Resurrect Pages and 404: Page is Not Found? Now it will be! can help in such scenarios. While Resurrect Pages relies on several popular page cache sites, 404: Page is Not Found uses the Wayback Machine at Internet Archive to serve the dead pages.

Extension series

To install each extension, click the shiny green Add to Firefox button on its homepage. After the customary browser restart, you'll find the extension available from the right-click context menu. You can even customize Firefox's menubar to sport icons for these extensions if you like. Right-click the menubar and click Customize. Scroll through the available icons, and when you spot the icons for the extensions, drag and drop them onto the menu bar.

The 404 extension uses the Wayback Machine at archive.org to show you a cached copy of a dead page. However, you can use the context menu entry for the 404 extension to view a cached copy of any page. Browse to any page or Web site, right-click anywhere in the main Firefox window, and click Find archived page. The 404 extension looks for the 404 Error code in the HTML tag of the missing page before loading the cached copy. The extension will not load the cached copy of a page if it doesn't find the 404 error. In such cases, you can use the context-menu entry as described above or click the menubar icon.

The extension currently recognizes almost a dozen error messages, including 404, HTTP 404 Not Found, HTTP 404 Error, 404 Error, 404 Not Found, and 404 File Not Found. The 404 extension pops up a confirmation message if it encounters any of these messages on a Web page. When you click a missing link, the extension will report this message: 'Page Not Found' was detected at 'http://slashdot.org/dog'. Click 'Cancel' if this is an error and this warning will not appear in the future for this page, or click 'OK' to see archived version of the page.

If you click OK, the extension will load an archived copy of the page. Sometimes the extension can err and falsely identify a page as missing. In such cases, you should click Cancel; that will add the page to a whitelist and avoid future false detection for that page.

Unfortunately, the 404 extension has a severe flaw: It loads the oldest cached page it finds in the Internet Archives. If you wish to view the archived copy of a page, instead of showing you the most recent archive, it loads the first. So, if you visit a page today and load the archive, the page that comes up on your screen may well be a few years old, depending on when it was first archived.

Resurrecting Pages

While the Resurrect Pages extension has the same basic idea as the 404 extension, its execution is far superior. The extension works with many caches, such as CoralCDN, Google Cache, Yahoo! Cache, Internet Archive, and MSN Cache.

Using this extension is just as easy as the 404 extension. Anytime you run into a page that is no longer available, the error page itself presents the option to select one of the caching mirrors to view an archived copy of the page. Clicking on any of the cache mirrors will open the archived copy of the page in a new tab. You can also view the cached archives of any page if you right-click the main window in Firefox and then click Resurect this page. This brings up the Resurrect dialog box, from which you can choose to view the archived copy of the current page in the current tab, new window, or new tab. After you've selected one of the mirrors in the list, click OK and Resurrect Pages will display the archived page.

If the mirror you selected does not provide an archived copy of the page, choose a different mirror and try again. Unlike the 404 extension, when you use the Internet Archive, this extension will show you all available archives of the page, and you can select the one you'd like to see.

Sadly, this extension too requires some polishing. The Resurrect Pages extension can't remember your preferences. Every time you wish to see an archived copy of a page, you have to select whether to open the archive in a new tab, new window, or the same tab.

Still Resurrect Pages is obviously better than the 404 Page is Not Found extension, thanks to its use of multiple caching mirrors and the option of choosing any cache from the error page itself.

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