My favorite feature of Opera is unique to the extent that it's preventing me from switching to any other browser. The feature is Spatial Navigation. The ability to navigate links and other elements on a web page using only the keyboard in an intuitive manner, that doesn't require a small number or hint displayed next to each one.

Simply use Shift and the arrow keys to move to the closest link in that direction.

It's a lifesaver, it's unique and it's indispensable.

The incredible speed with which Opera responds when you click the back button (or, more likely make one of the back gestures).

A bonus for advanced users who are familiar with using User JavaScript in Opera:

Opera uses some heuristics to make sure that the history navigation keeps all the scripts working. This means that some sites don't use the super-snappy history navigation mode.

If you're sure that a particular site doesn't need the full page rebuild, there's a method you can in UserJS that tells Opera that fast history navigation will work:

opera.setOverrideHistoryNavigationMode( 'fast' );

If you're sure that all the sites you ever visit will work with this mode, you can change the History Navigation Mode setting to 3 (fast mode - the default, 1, is automatic mode). You can get there by typing the following into Opera's address bar:

opera:config#UserPrefs|HistoryNavigationMode

Note that setting that option is actually very unlikely to work for all sites you browse... Opera's knowledgebase has more details ^[1] about why this option is necessary.

Mouse gestures!

http://www.opera.com/browser/tutorials/gestures/

Speed Dial ^[1]! It's a way of providing quick links to commonly visited pages, which are customizable (unlike Safari's Top Sites).

It was introduced in Opera 9, with a max of 9 pages, but this has been increased to a maximum of 25 in Opera 10 to allow different layouts, making more use of the available space dependent on resolution (for example, I find the 4 x 3 layout better for my MacBook because of the widescreen screen).

I also really like the shortcuts; on OS X it's ⌘+1 - ⌘+9 (for sites 1-9) and Ctrl+1 - Ctrl+9 on Windows - this makes it easy to open up all my commonly used sites when I open Opera.

Here's a screenshot:

Zooming that actually works correctly. It not just increases/decreases font size like Firefox.

Fast back

Opera caches pages in memory (not just the code, but the fully rendered version) so that when you go back they load instantly. No other browser comes close to this. Combined with Opera's Rocker Gestures (right+left click, left+right click) and its generally fast load times, makes for super-quick browsing!

It's very simple to create a "custom search" so you can submit a (search) form from the address bar with a letter or two followed by the search terms. It's very useful for executing searches on sites you search often. It saves having to load the search page, first.

For example, by default you can enter "g widgets" in the address bar to search google for "widgets." You can add your own custom search by right-clicking on the input field of a form and selecting "Create Search..."

Hint: create custom searches for SuperUser.com and StackoverFlow.com^^

Tabbed browsing. Yes, all the others now have that too, but with Firefox, e.g., I often end up with several browser windows. In Opera, everything is a tab.

I consider alternative rendering modes and options as Opera's uniquely powerful feature. True you can get all the same goodness in other browser with plugins, but having it working out of the box is sometimes sweeter.

Opera allows you to tweak a page's rendering to your heart's content:

• small screen
• high contrast accessibility
• BBS-style emulation
• collapsed tables
• styleless and imageless
• a combination of all the above

The "Block Content" feature. It is nice to have a built-in way to remove banner ads from a site.

Fast Forward

Opera finds the next page in a sequence and you can browse to it using the fast forward button or forward mouse gesture.

Most useful on Google search pages, you can skip through dozens of results in a few seconds.

It can also be used to browse through every file in a directory listing without going back. In other words, the FF button goes Directory Listing > Image 1 > Image 2 > ... > Image n > Directory Listing

Another feature I really like is the Opera Wand; this is a tool which remembers login credentials for websites, and can auto-complete them for you whenever you return. I only use it on my home PC where I know that there's not a risk of someone accessing real important data.

I also really like the ⌘+Enter (and Ctrl+Enter on Windows, I believe) shortcut. I'm not too sure whether the Wand was a feature unique to Opera when it was first implemented, and it's obviously not unique now, but I've been using it for many versions and it's a must have!

Well.. it's fast!

Not exactly a feature, but this is what I like about Opera.

Its sub-one-percent marketshare ^[1], so one doesn't often have to argue with fanboys ;-)

Duplicate this tab

The new tab will also duplicate the history.

Built-in RSS Reader

The built-in RSS reader in Opera is the best RSS reader I have used. It's really nice not having to have another program open to check RSS.

There are no unique features left that only Opera features. But many ideas on browsing the web came from Opera, like speed dial, mouse gestures or tabbed browsing (not sure if Opera invented this, but I first saw it in Opera).

But I never foresaw mouse gestures work that well. Man, I love this Feature. I often catch myself trying mouse gestures in the Windows Explorer.

The 'show images' button, great for slow pages or ones full of ads.
It's buried about 4 menus deep in IE, there is an addin for Firefox but it is unusable.

Ability to select a URL (that was not made into a link), right-click and choose "Go To Web Address"

Doing the same on plain text will use the selected words as the search terms in your default search engine.

The ability to arrange and tile tabs. (I know, there's a Firefox extension for this, but it seemed slow and clunky to me last time I tried it)

Precision : The fact in general that the Opera window is a virtual desktop, in which tabs are internal windows. Thanks to that, the eventual popup window stay in the Opera "space", it won't go populate the Windows taskbar.

Closed Tabs, so you can reopen the recently closed tab without digging into history. It saved me days!

Resource Scalability. I frequently have 30+ tabs open and Opera still works fast and doesn't use more than 400-600 MB of RAM. Firefox gets much slower with a larger number of tabs.

Syncronization. This way my work and home PC all have the same bookmarks/notes/speed dial/searches.

Opera Unite ^[1], easy and fast way to host a file server, webserver, media player, chat, photo gallery, directly from your personal computer. (No more hosting on obscure distant servers to show photos to family, or share a file...)

The Copy to Note (Ctrl+Shift+C) functionality, very useful for quickly storing content off a page for later reference without having to open up another application or bookmark the page.

I often use the "Go to parent directory" command. It's not available via the UI but you can use the mouse gesture "GestureUp, GestureLeft". Pretty helpful sometimes.

I personally love Opera Dragonfly, the web editing helper tool that comes with Opera. You don't need to download any special features or anything to get it.

May seem like a tiny, little detail, but Opera will follow a link only after I have released the mouse key. This has probably saved me days because I didn't follow links that I didn't really want to follow.

The panels. By hitting F4, or View -> Toolbars -> Panels, I can bring up some useful information. The one I use most (being a person who often had multiple windows open, each with two dozen tabs), is the Windows panel, where I can select a number of open pages and close them all easily. The links panel is also often handy if I'm trying to download several things from one site.

I really like the way email is stored in the Opera mail client. There are no folders but everything is indexed so you can find anything instantly by typing a few search terms.

Ability to search in the browsing history (previously opened web pages).

HOW-TO: enter the following in the address bar and hit enter:

opera:historysearch

Then enter the words to search for in the search input field and press the "History Search" button.

Text resizing/zoom. I love that it is only a few keypresses (Shift-Cmd-Plus and Shift-Cmd-Minus on my Mac) to increase (decrease) the font size. I will often set it up to 150 to 200% to make for easy ready when I'm not sitting directly in front of the computer.

Smooth Scrolling via middle click

It's very granular and can scroll 1 pixel at a time (even sideways).

The latest versions of the Firefox, Chrome and IE still don't have this right, though FF is close.

How about the fact that most - if not all - of these features are built in?

What I like is "create follower tab" - a new page in which you can open the links you click in the original one. Of course it's nicest when you have the two tabs side by side - with Opera being an true MDI browser organizing pages this way is a piece of cake (tile horizontal). A nice way to keep a document's index (often at the top) and it's contents side by side.

Copying parts of a hyperlinked text is a very nice feature. Example; Try to select 'select' inside this sentence. ^[1]

The mouse gestures feature is one that I find particularly useful.

I started using Opera because at the time, all of the other browsers seemed to have a persistent problem of going to 100% CPU for a period of time when visiting certain sites. Once I got accustomed to the mouse gestures, they made it quite easy to do certain things very quick and efficiently.

BitTorrent - No need to use a separate torrent client application!

I also like "open link in background" very much. It's in the right-click menu, you can also configure middle-mouse cick to it. You can keep on browsing the page you're on while opening up the pages you also want to view.

Inline search

The ability to search through the text or the links within a page using . or ,, respectively.

No one mentioned one of the killer features Opera has. Ever spent half an hour replying to someone's post in the forums, hit submit button to see message saying that you session have expired? With other browsers your cursebox gets richer, while Opera user just smiles and hits back button. Yes, Opera preserves forms entries in tab history, real time saver!

Customizable UI. The default UI setup is (imho) very poorly chosen, but it can be customized a lot.

I always get rid of unnecessary toolbars and buttons and move the tab panel to the right.

The "g \text" to search on Google for \text. I also have chem and elem set up for when I'm doing chemistry homework and a few more for coding in various languages. I'm so used to it that when I use Chrome ^[1], I end up typing "g " even when I'm not trying to.

It also allows me to remove the Google search bar and have more room for custom buttons (like the ones I have that increment the last number in the URL, for pages that fast-forward might miss).

I know that Internet Explorer has this feature as well now, so when is it going to work well in Firefox?

The Notes and History panels. Firstly they are both built-in and not some un-stable add-on.

The History panel, with quick find, sorting, By Site/By Time, is the simplest way I've seen in any browser to find a specific page you didn't bookmark but visited last week.

Not really a feature as such, but the main reason I'm using Opera as my main browser and the reason I switched to Opera in the first place is the layout of the interface, and more generally how userfriendly the interface is: Everything is exactly in the right place, with a minimum of mouse movements necessary. In other browsers I need to move the mouse all over the place, e.g. refresh / stop button on the right, back/forward navigation buttons on the left, home button somewhere else, ... In Opera everything is together and is in exactly the right place (next to address bar).

Other features that improve usability are the jump to previous site (next to the back button), Opera sync (so bookmarks are always the same on all PCs), RSS reader, mouse gestures, navigating one level up, wand passwords, and many more that have been mentioned by others. And if everything breaks and a site doesn't work with Opera (not very common), simply right click and choose "Open with..." to open the site with another browser

I love adding lots of custom buttons from the Opera Wiki, especially 'Kill' and 'Smiley Identify', and the way you can move just about any button or option to almost anywhere else :D

http://operawiki.info/CustomButtons

I like to park my Speed Dial pages on Forums I frequent multiple times in a day. I set the auto-update to around 5 minutes and all I have to do is browse my Speed Dial to see if there's any new forum posts for all sites. I know there's other notification options available but this works for me well.

The best feature? Un-installing Opera for a better more reliable browser! There is nothing in Opera that I can't get in other more stable browsers.