Portable Firefox

Mozilla Firefox is an open source web browser with a clean design, providing excellent browsing speed and very powerful customization tools, with just a reasonable footprint on computer resources.
Portable Firefox is a special edition of Mozilla’s browsers that can be carried on a removable drive and run on any computer without affecting its system registry. There are no differences between the portable and the standalone editions in terms of functionality or appearance.
Firefox bundles features that include smart bookmarks, spell check, private browsing, a download manager, incremental find, tab grouping (gathers related tabs and organizes them into groups) and several others. In addition to these, Firefox also accommodates a series of tools for developers, such as the DOM Inspector and the Error Console.
The first contact with Firefox shouldn't be surprising since most browsers have already adopted tabbed browsing. It comes with a tabbed interface so opening multiple pages at the same time isn't a problem anymore. But what's under the hood is what really makes the difference.
Firefox is amazingly fast and blocks pop-ups, some viruses and spyware, but also gives the user an extraordinary power of customization through a well-developed add-on manager. Basically, you can change almost everything in your browser, starting with the way it looks and ending with features and functionality.
Mozilla lets you install new themes and so-called Personas that change the appearance of the main window, as well as add-ons (created by third-party developers) for adding new functions to the application.
Firefox Sync is another feature worth mentioning; it enables you to synchronize browser bookmarks, passwords, forms and add-ons across multiple computers, by storing all of these on the dedicated Mozilla servers. The data is encrypted, so no other person, aside from you, is granted access to it.
Firefox is fast and reliable and includes a decent set of customization tools. With the aid of a few add-ons and themes, it can be tailored to the needs of day-to-day users, as well as developers.

Firefox Video Guide