While Firefox is widely known, the Opera browser may need an introduction. Opera is known for its speed and its multitude of features. It's available for a wide range of platforms; in addition to Linux, Mac OS X, and Windows, Opera runs on FreeBSD, Solaris, Windows Mobile, and OS/2, among others.
Opera includes an embedded chat client and mail client, the latter of which includes support for RSS news feeds. (In this review, I will focus only on the RSS features of the mail client, for the sake of a fair comparison with Firefox, which lacks email capabilities.) Because it's not open source software, Opera has no "extensions" like those of Firefox. Despite being closed source, Opera is very customizable, via both the preferences menus and the manipulation of the plain-text configuration files.
I tested Opera and Firefox on SUSE Linux 9.1, Mac OS X Panther, and Windows 2000.
Look and feel
The user interfaces of the two browsers are strikingly different. By default, Firefox has a clean interface, with only the basic necessities (back, forward, reload, stop, and home buttons, an address bar, and Google search). Opera, on the other hand, displays many more tools and buttons by default. While this may be more daunting to a new user than Firefox's clean interface, the standard buttons are easy to find. The advantage with Opera is that a first-time user can see many of the unique options that Opera offers, which they might not know about otherwise.
Both exhibit consistency of interface, but in different ways: Opera's default look and feel are for the most part consistent from platform to platform, whereas Firefox's default look and feel are for the most part consistent with other applications on the platform (though both applications allow users to customize their interface and install themes or skins). Either of these properties can be seen as a strength or a weakness. For instance, someone who works regularly on multiple OSes may prefer Opera, which looks and acts much the same on each machine. Someone who works regularly on one OS may prefer Firefox because it looks and acts more like other applications on that platform.
Firefox and Opera also have different menu structures and occasionally incorporate different keyboard shortcuts for common tasks like opening a new window or a new tab. In most cases, Firefox is more consistent with "standard" shortcuts and menus than Opera is (i.e. Firefox's shortcuts are more often the same as those of Safari, Netscape, or IE). The differing Opera shortcuts and menus are not difficult to learn, but they may be a stumbling block for users beginning with Opera or going back and forth between Opera and another browser.
Ultimately, though, look and feel are about preference. I like Opera's look better than that of Firefox, but I prefer Firefox's consistency of functionality with other applications on the host platform, particularly in adopting standard shortcuts.
Default features and customizations
One also sees a strong difference in philosophy between Firefox and Opera in their default configurations. To avoid bloat, Firefox developers created a browser that is lean, fast, and by default includes no extraneous features or closed source plugins. This makes for a small application download and a fast browsing experience, though there are hundreds of plugins and extensions that a user can find and install with relative ease. The biggest downside to this approach is that Java and Flash are not installed or enabled by default. Opera, on the other hand, does not provide extensions, but includes many more features by default, including Java, Flash, the optional disabling of sound and GIF animation, dictionary search, the automatic filling out of forms, identifying itself as a different browser, reloading pages at regular intervals, URL filtering, and paste-and-go URLs in the address bar. Thus, of the two, Opera is the browser that provides the most functionality upon initial installation.
While it's important to note what each browser can do "out of the box," both browsers are known for their customization, and Firefox in particular is designed to be extended. I ran some tweaks on each browser and installed some Firefox extensions, to try to get a more complete and realistic impression from each browser. Most default features in Opera that are not part of the default Firefox installation can be installed into Firefox as plugins or extensions, including all of those noted above. In fact, there are more than 400 extensions for Firefox that add to the browser's functionality, and advanced users have the opportunity to write their own extensions and share them with other users. This customization method gives a lot of power to even novice users.
Opera, on the other hand, cannot be customized by extensions, but it contains many more options in its Preferences menus than most browsers, and the Opera Community site contains a large number of skins (comparable to Firefox's themes) and language packs for downloading. Opera can also be customized by editing its configuration files. Though the application is closed source, Opera developers have not applied proprietary code to many of their configuration files, allowing advanced users to edit them manually or through a script, to make use of more advanced features like URL filtering or adding additional email tags and labels to the mail client. This gives more control to power users than other proprietary browsers do, but it is not as easy to use as Firefox extensions, especially since the smaller Opera community has not generated as many scripts and helper applications as the Firefox community has generated extensions.
Ad blocking is a good practical example of this. In Firefox, no ads -- except for pop-up ads -- are blocked by default. However, there is an adblock extension, which allows a user to choose specific images, files, and scripts to block, as well as wildcarded URLs (such as "*/ads/*"). After a short time (in my case, just a week or two), one can accrue a list of URLs (with wildcards) which will block most ads on the sites one visits regularly. There is also an extension that automatically disables all Flash items, replacing them with a "play" button, allowing a user to pick only the Flash items he wants to view. These items are easy to install and to use, and they can drastically improve -- and speed up -- one's browsing experience.
Opera, on the other hand, has a configuration file where one can create a list of URLs to block, which also allows wildcards. If one has a good list (say, exported from the Firefox adblock extension), one can add it to this file and have most of the ads removed on the pages one visits most often. However, it is not as convenient to add individual items to this file as in Firefox. There is a third-party application that updates this file to match a regularly updated list available online, and it allows users to add their own URLs as well. This works well, and the list is well-maintained, but it is available only for Windows, and being a separate program, it does not allow a user to simply right-click on an item in a Web page to add it to the list, as Firefox's extension does. Like Firefox, Opera does block pop-up ads, but as for Flash, Opera does not have as convenient a tool as Firefox. It can, however, filter out URLs for specific or wildcarded Flash items and it can disable Flash completely with a choice in the quick preferences.
With many features, like ad blocking, the difference between Opera and Firefox is really a matter of convenience. In most cases, both browsers can do many of the same things. If, for example, your browsing experience typically requires features that are provided by default in Opera but not Firefox, Opera will likely be more convenient. However, if neither browser includes some of the features upon which you rely by default, and a Firefox extension already exists, Firefox will likely be more convenient. I hope more users and developers will write scripts for Opera that are comparable to some of Firefox's extensions; if they do, the playing field may begin to even out.
Opera incorporates several features with no counterparts in Firefox. For example, when one clicks in Opera's address bar, a dropdown menu offers links to the home page, the 10 most visited sites, bookmarks, an Amazon.com search, and a price comparison search. This nice feature can be a time-saver if you use it, but if you don't, it does not interfere with your browsing. Opera's mail client automatically detected and imported my address book contacts (on the Mac only), and whenever I made a change to the Mac's address book, Opera picked it up. (I was disappointed, though, to find that changes made to the Opera contacts did not make their way to the Mac's address book.) However, my favorite feature unique to Opera, and one I would like to see more applications incorporate, is quick preferences.
Invoking quick preferences (by pressing F12 in Linux and Windows, or selecting Quick Preferences in the Mac's Opera menu) brings a short list of preferences commonly used or changed, especially upon first installation. Critics have often complained that Opera was too complicated for an average user. Quick preferences is a response to that concern, and it's a great way to make the application a little easier without removing any of its advanced functionality.
RSS news readers
Both browsers include RSS news readers by default, but they are quite different. Firefox uses Live Bookmarks. By clicking on the RSS icon in the status bar when visiting a site that has an RSS feed, one can subscribe to the feed and see the regularly updated headlines in one's bookmarks list. Opera too has an RSS icon (though in the address bar), and clicking on this icon subscribes the user to that news feed. Opera, however, uses its mail client as the news feed reader, and the headlines, synopses, and links to the articles are delivered to the feed's mail folder, where they can be tagged, searched, and saved for future research.
Both of these methods have their advantages. I prefer the Opera method for tech articles. I am more likely to browse through all the tech articles than I am regular news articles, and if I don't get around to reading them right away, the links will still be in my inbox where I can find them later. Once I read them, I tag the ones I may refer back to at a later time, and I can search the headlines and abstracts for the topics I am researching. On the other hand, I prefer the Firefox method for regular news sites). I can quickly see the headlines of the day and decide what articles I want to read. I am not likely to save these articles for future reference or searching, nor am I likely to look at news from several days previous (which has been bumped from the list), so I don't need an inbox in which to keep those items. (On the occasion that I want to save an article, I can always bookmark it.)
Overall, I have been happy with both Opera and Firefox. Both are rich in features, and though only Firefox is open source, both browsers offer many options for customization beyond mere cosmetics. I cannot say that one browser is superior to the other. If one is willing to consider both open and closed source options, than picking one of these browsers over the other will likely come down to issues of convenience, personal preference, or the particular tasks one typically uses his browser for. One user may choose Opera for its one-time install with no assembly required, while another may choose Firefox because of a handful of extensions he simply cannot do without. Perhaps Opera's integrated mail and chat clients or method of RSS implementation will win over one user, while another will gravitate towards Firefox's lack of banner ads and choose Mozilla's Thunderbird for email.
As for me, I'll be sticking with Firefox as my main browser for now. All else being equal, I prefer to use an open source application, and there are some Firefox extensions that I really miss when I'm on Opera (notably Adblock, GooglePreview, Linky, and the Web Developer toolbar). On the other hand, I'll likely keep using Opera at work, where most of my browsing involves RSS news feeds and other forms of research. Others, however, will make different choices. At the end of the day, both Opera and Firefox are excellent browsers, with a lot to offer any user. No one has to settle for the default, and Mozilla and Opera are both doing their part to see to it that no one does.