Firefox's network error pages ask me a bunch of questions that Firefox could answer more easily than me. For example, here are the four questions Firefox asks me when I point it toward http://example.example.com/, and ideas for what Firefox could do instead of asking me questions: 1. Did you make a mistake when typing the domain? (e.g. "ww.mozilla.org" instead of "www.mozilla.org") --> If it's definitely a typo (e.g. www.mozilla..com), fix it for me (bug 175634). --> If it's probably a typo (e.g. ww.mozilla.com), give me a prominent link with the typo corrected. --> Offer to search Google for the hostname. The user might have been trying to search to begin with (bug 273155), or Google might be able to correct a subtle typo (e.g. http://www.google.com/search?q=fivethirtyeigth.com). 2. Are you certain this domain address exists? Its registration may have expired. --> Offer to search Google for the page's supposed title, if I got here by clicking a bookmark. --> Offer to take me to the corresponding archive.org page (bug 196227). --> Offer to take me to the corresponding Google Cache page (bug 195164). --> Tell me if the domain appears to be registered or not (bug 399129?). 3. Are you unable to browse other sites? Check your network connection and DNS server settings. --> Indicate the type of DNS failure: "can't find a local DNS server" is clearly a local issue while an authoritative "no such hostname" response is probably a site issue. (Requires bug 196076) --> Give me a button that kicks off a few DNS lookups and tells me whether DNS is working. --> Give me some links to other sites, or a button that tries to load www.mozilla.com and reports the result. --> Give me a button to open my OS network settings. 4. Is your computer or network protected by a firewall or proxy? Incorrect settings can interfere with Web browsing. --> Give me a button to open Firefox's proxy settings. --> If I'm running a software firewall that Firefox recognizes, give me a button to open its settings. (cf bug 308982)

In addition to adding buttons to the proxy page (which is bug 484215, already a blocker), it would also be useful to add information to the error page about the proxy server (bug 380526).

Just wanted to mention that a Labs experiment, bug 552992, is related to this, as it involves prototyping Firefox-Herdict integration. Not adding it as a blocker, though, since it's a Labs experiment (addon) and not a change to product.

Moving this to Core:Document Navigation since it is a UI-level feature and Necko doesn't or shouldn't do UI. AFAICT, the error pages are part of DocShell and definitely not part of Necko.