When comparing Opera vs Dolphin, the Slant community recommends Opera for most people. In the question“What are the best Android web browsers?” Opera is ranked 10th while Dolphin is ranked 18th. The most important reason people chose Opera is:
The built-In adblocker is faster than any extension. It's possible to add your own filter lists. However, the adblocker isn't enabled by default.
Specs
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Pros
Pro Built-In Adblocker
The built-In adblocker is faster than any extension. It's possible to add your own filter lists. However, the adblocker isn't enabled by default.
Pro VPN onboard
Free VPN onboard (but it's slow and it leaks your IP), includes Germany, Canada, USA, Netherlands, Singapore.
Pro Video pop-out feature
You can pop-out any video and it will stay on top while you are surfing on other tabs.
Pro Compatible with Chrome extensions
Since Opera is built on Blink, the same engine Chromium is built on, it was possible for Opera developers to allow Chrome extensions to run in their browser.
Pro Strong HTML5 feature support
Opera scores highly on HTML5 feature support.
Pro Opera Turbo
Opera has a functionality called Turbo which increases browsers speed and reduces data consumption considerably by compressing the data that's found in a web page.
Pro You can install extensions on the sidebar
Unlike other browsers, you can install add-ons such as tabs, bookmarks, history, sessions, notes, and extension manager in the sidebar. So you have the flexibility to use it for your purpose.
Pro Opera Sync
Opera Sync allows you to synchronize your bookmarks, passwords, and more from any computer, phone, or tablet.
Pro Customizable
Opera is full of user controlled settings. Everything can be imported and exported even RSS feeds. It can be skinned in a variety of different themes or it can be extended through the use of a large number of plugins available.
Pro Battery saving mode
Pro Opera can have extensions from Opera Addons & Chrome Store websites
Opera supports cross-browser extensions. Opera Addons site keeps quality up compared to Chrome Store. Full of useful extensions, Opera also supports extra APIs like Speed Dial API, Extension Sidebar API and Stash API meaning wider variety of extension possibilities than in Chrome.
Pro Speed Dial
Opera's Speed Dial (new tab page) has the ability to hold as many websites as you want, and you can customize it almost however you want. You can also organize the websites on the Speed Dial into folders.
Pro Partly open source
Source code available on GitHub.
Pro Blazingly fast
Scores top on Basemark.
Pro Portable
You can save the Opera's setup files on a USB hard drive and run its portable version anywhere.
Pro For Opera 2017 & 2018 gonna be time of new
Opera got Reborn UI as the first implementation from Opera Neon concept browser. Snap -feature is next. Opera constantly improves its basic functionality - unlike Chrome.
Pro Free vpn
Without any cost unlimited and working.
Pro Lightweight
It doesn't consume much RAM, unlike Chrome.
Pro Touch bar support
Pro Built-in currency converter
Just highlight price on a website and see this price in your currency.
Pro Fast video loading
Opera loads videos faster, making it useful for slow internet connections.
Pro Immenseley configurable
As with any KDE app, Dolphin, allows adding or modifying toolbar buttons and keyboard shortcuts.
Pro Can split views
Dolphin supports splitting the view in two navigational areas, this way you can navigate two different directories at the same time.
Pro Integrated terminal
Pressing F4 with any opened folder on a mounted path opens a console within dolphin.
Pro Also has a refresh option
Dolphin is without a doubt the best fully functional and easy to use and multitask with.
Dolphin also has a refresh button which no other File manager has. It's great for tracking a large files transfer; that's what file managers are for - good common sense.
Pro Easy to extend with plugins
Dolphin follows KDE's philosophy of being extendable and configurable. It can easily be configured and customized through plugins.
Pro Auto mounts flash drives
Dolphin automatically identifies and mounts external flash drives.
Pro Fast at opening graphics folders
Pictures with or without previews is optional and selectable at the touch of a button.
Pro Does not use third party libraries
Unlike all those GTK-based file managers it does not have to rely on external written software for its functionality because KF5 is KDE SOftware and developed alongside.
Pro Keeps its state
It starts with last opened folders.

Pro Fully supports HiDPI
Supports HiDPI displays.
Pro Automatically centers items
In icons view mode, the space between files gets stretched so that there is never and annoying empty space at the right side of the window.
Cons
Con Owned by a Chinese consortium
Who certainly need to conform with Chinese government requirements to let them infiltrate everything you do online.
Con Trash VPN (Slow and Leaks IP address)
Terrible VPN service. Super slow. It's just a proxy service that leaks your IP address, not a VPN. Not recommended!
Con Cannot select tabs
Unlike in Chrome and Vivaldi, one cannot select multiple tabs to move to another/new window.
Con WebKit/Blink is not customisable or lightweight
Opera is built on WebKit/Blink, which means it shares cons of Chromium: high RAM usage (Not lightweight), lack of customizability.
Con Uneditable default search providers
It can not delete or replace already built-in search services such as Yahoo, Google, DuckDuckGo, and Wikipedia.
Con Proprietary
While Opera is currently available gratis (without monetary charge), it is currently not libre (meaning that it does not allow users to view the source code used to create, to modify that code, or to redistribute modifications) and is therefor neither free nor open-source software.
Con Unable to sync extensions
Imagine having 100 extensions and Opera link cannot sync them, which will be troublesome.
Con No address bar in fullscreen mode
Unlike in Vivaldi.
Con Buggy
Some buggy or confusing behavior with the bookmarks bar and moving tabs, and entire windows turning black after a while.
Con Same security-holes as Chrome
Opera uses the same browser engine as Chrome, meaning it has the same security-holes as Chrome. Chrome is a big target for hackers (being the most popular browser in the world), and a webpage that will hack Chrome will also hack Opera.
Con No reader view
There is a great reader view extension which is available.
Con Built ad-blocker works when it wants
Con Basically a Chrome clone
The latest versions of Opera are basically Chrome clones, so they really don't add anything new.
Con No menu bar
Con The advertisements are terrible
There are too many advertisements in this browser.
Con Extension icons not directly moveable
Con Cannot stop auto update
Con Needs user prompt to install from Chrome web store
Every time you install an extension, you need to say install first from Opera extension list to proceed.
Con May be a little slow on startup
Dolphin can be a little slow on startup (depending on distro, hardware etc...). Startup time can vary from a couple of seconds to up to a minute.
Con Can hang on remote file systems
It doesn't cope well with remote file system nicely like sshfs or any samba, like when network is not responding/very slow. It just hangs.
Con "Type" column too verbose
Despite having a large enough monitor, if you keep the size of the browser window small, the "Type" column (in "Details" view mode) insists on including the complete multipart MIME string, making the column so wide that trying to limit its width makes the column useless. Sorting by "Type" renders the list into an incomprehensible mess.
Con Poor optimization on later versions
Con Too simple
Feels weird on KDE because it has less customizing options Konqueror and any other KDE app have.
Con Can't perform ROOT actions
Developers set a constraint in Dolphin that deny Dolphin to run with root permissions. Hence, if you want to perform an action that require root permissions, such as rename a file in /etc/ folder, you are forced to use terminal or switch to another file manager.
