Firefox/URL Bar Algorithm

This page documents the steps Firefox takes as a user types some text into the URL bar, and when they press "Enter" or "Go".

While The User Is Typing

From the very first character typed, we dynamically search:

• history titles and URLs
• bookmark titles, URLs and tags
• open tabs titles and URLs

with search results limited to some subset of those sources if requested, according to this algorithm.

When Enter Is Pressed

(Adding a Ctrl or Shift modifier changes the behaviour; the below is the unmodified algorithm.)

Before Network

Function getShortCutOrURI in browser.js.

• If the string contains a space, split on the first space and examine the first token.
• If it's a search engine keyword, expand using the relevant search URL.
• If it's a user-defined keyword, expand that.

...

• If it looks like a search according to this algorithm, insert it into the keyword.URL preference value to produce a search URL, since the keyword.enabled preference defaults to true in Firefox.
• The algorithm says it's a search if it contains a space or a quote before the first dot, colon or question mark, or if it starts with a question mark.

...

• If we're looking at something that does not have a scheme specified, prepend either "ftp://" or "http://" depending on whether nsDefaultURIFixup::IsLikelyFTP returns true.
• Try to construct an nsIURI. If that fails, fall back on producing a search url from keyword.URL, since again keyword.enabled defaults to true.
• Start the network load.

Network

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