When comparing Mozilla Firefox vs Opera, the Slant community recommends Mozilla Firefox for most people. In the question“What are the best desktop web browsers?” Mozilla Firefox is ranked 9th while Opera is ranked 24th. The most important reason people chose Mozilla Firefox is:
Firefox [scores strongly on HTML5 feature support](http://html5test.com/results/desktop.html) Though not as strongly as Chromium/Chrome browsers do.
Ranked in these QuestionsQuestion Ranking
Pro Strong HTML5 feature support
Firefox scores strongly on HTML5 feature support
Though not as strongly as Chromium/Chrome browsers do.
Pro Free, open source and community driven
Firefox is available as a free download. All Mozilla software is licensed under the Mozilla Public License. Instructions on how to obtain the source code can be found here.
Pro Syncs between devices
Firefox Sync is an optional feature in Firefox that allows syncing bookmarks, passwords, and add-ons between devices.
Pro Respects your privacy
Mozilla is one of the first browsers that advocates privacy. They believe that internet should be in the user's control and not those who run the websites, and so they give tools inside the browser to make the user be more in control.
Pro Strong developer tool
The built-in developer tools have been merged with the popular FireBug extension since FF57.
Pro High performance
The Firefox Quantum update (FF57) greatly increases the render speed and general performance of the browser, by taking better advantage of the user's hardware.
Pro Reader View
Reader View in Firefox allows users to read an article without any distractions by removing ads, unrelated elements and other distractive objects (similar to Microsoft Edge's Reading Mode and Safari's reader mode).
Pro Good font rasterizing
Font rasterizing on Windows is much better than in competitors. Even smaller text is clear and contrast.
Pro Tagging bookmarks
Firefox is one of the few browsers that you can tag your bookmarks. You can view a list of tags and can search your bookmarks in the address bar with tags.
With new integrations focused on security and performance, Firefox is faster and less likely to have problems during use than ever before.
Pro Dark theme
Beyond the toolbar and tabs, it darkens UI elements such as the URL-bar, pop-downs, new-tab page and more.
Pro Automatically updated
Firefox is automatically updated on the platforms where it makes sense.
Pro Awesome customizability
Great library of add-ons.
Pro Uses less resources
Firefox 57 (Quantum) and newer uses less resources than ever. It is proven with benchmark done by AppleInsider.
Pro Open Source
Open Source means that you can see the source code. So everybody even if they don't work for Mozilla is able to look what the browser does in the background. So you can be 100% sure that Firefox doesn't have hidden "spy features" unlike Google Chrome.
Pro Screenshot tool
Powerful screenshot tool built right into the browser.
Pro Fast bookmark management
In order to add an open page to the bookmark bar, the tab can be dragged down and is added immediately.
Pro Ethical and pragmatic company mission
The Mozilla Manifesto outlines the company's mission and principles. Paraphrasing, they want the Internet to be a free and open resource, and to enable individuals to get the best use of that resource. They do this by creating open source software to which anyone may contribute, so long as such contributions fit with their principles (both ethical and technical).
Pro One of the few browsers not using Chrome's Blink engine
Firefox uses its own rendering engine (called Gecko), instead of Google-controlled Blink like the vast majority of other browsers.
Pro Really independent browser
It's not dependent on Google.
Pro A lot of add-ons
An enormous number of add-ons.
Pro Text-to-speech (with adjustable speed) without add-ons
Firefox Reader Mode includes Narrate, a feature that adds text-to-speech functionality to the browser.
Pro Lower memory fingerprint than competitors
Firefox used to be a trailer in memory usage, but as of 2017 it's less hungry for memory than competitors like Edge, Chrome, Safari and Opera.
Pro Built-in Privacy Protection
Blocks tracking cookies, finger print scanners and Cryptominers by default. Can be changed to the user's individual needs.
Pro Firefox Experiments
FF Experiments are Mozilla projects available from FF Test Pilot, such as Firefox Colour, witch lets you customise your browser theme to your liking!
Pro Firefox Lockwise Password Management
Helps store your usernames and passwords. Lockwise also lets you know if any of the sites you have login details for have had their (and potentially your) data leaked!
The newer versions of it will soon use WebRender to render webpages, which'll make it much more efficient by utilizing GPU to paint webpages.
Pro HTML5 Video Preload
The only web browser that only preloads entire HTML5 video which is useful for slow internet.
Pro Integration with Pocket
Firefox comes with built-in Pocket integration that can allow users to quickly save the article for a read it later function to easily find any articles saved in Pocket from various sources and devices.
Pro Very Secure
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 and fast VPN onboard, 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.
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.
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.
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.
Con Some built-in advertising
With their new "pocket" feature, they offer advertisements built-in.
Con When you search in a website (Ctrl + F) there are no marks appearing in the right scrollbar
All Chromium based browsers have this feature.
Con Cannot directly translate page
Unlike Google Chrome, if you visit a website with a different language, you cannot translate it, which is a bad user experience for some.
Con Lack of keyboard shortcuts customization
Keyboard shortcuts can not be changed in a user-friendly way.
It is also difficult to manipulate addons with hotkeys.
Con Installs Addons with updates
Mozilla is installing/integrating addons with every update like the Mr. Robot promotion - it also has integrated Pocket that spams you every time you open the browser or a new tab with partners of Pocket.
Con Uses Google as its default search engine
Which is pretty ironic for a browser that's focused on "privacy".
Con GTK Themes styles the HTML forms
If you're in Linux and you use a dark GTK theme that uses white text and come to a webpage that forces black text on html-forms buttons you will get black buttons with unreadable black text.
Con Sometimes very buggy and slow
On sites like twitch.tv chat scrolling is still not fixed. Compared to other browsers Firefox is still very slow and feels sluggish.
Con Uses GTK on Linux/BSD
This makes the integration on non-GTK Desktop Environments very hard.
Con Partial dark mode (fixed)
Bookmark, context menu, etc. are not themed.
Con Multi Profile is not user friendly
Multi profile requires commandline -no remote to use and open about:profiles to create manually (on Chrome, you can instantly create them on right top user button).
Con Crappy license
Cannot redistribute binary after source code modification.
Con Doesn’t support multiple languages for spell check
If you write in multiple languages, you need to manually switch the spell check language.
Con Terrible user interface
And you can't even fix it anymore because they removed XUL.
Con False positives in virus-scanner
All Downloads in Firefox are scanned for viruses, but there are a lot of false positives.
Con Doesn't care for its original guidelines/goals
Mozilla originally aimed to be the "good guys" with user choice and privacy in mind. Their current leadership cannot be trusted to hold those goals in high regard:
1) Added Pocket - a privacy data sensitive plugin, made it mandatory
2) Tried to sneak in advertisement as "drive-by hack", backpedaled unconvincingly once users complained
3) Tried to randomly inject a small percentage of Firefox downloads in Germany with a data collecting plugin (Cliqz) that tech-savy Germans consider adware (no opt-out question asked).
Con It's a memory hog even though Mozilla claims it is not
Mozilla claims it's using 30% less RAM than Chrome but in real life tests it uses much more.
Con Owned by a Chinese consortium
Who certainly need to conform with Chinese government requirements to let them infiltrate everything you do online.
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 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 Cannot select tabs
Unlike in Chrome and Vivaldi, one cannot select multiple tabs to move to another/new window.
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 Extension icons not directly moveable
Con Uneditable default search providers
It can not delete or replace already built-in search services such as Yahoo, Google, DuckDuckGo, and Wikipedia.
Some buggy or confusing behavior with the bookmarks bar and moving tabs, and entire windows turning black after a while.
Con Cannot stop auto update
Con Trash VPN
Terrible VPN service. Super slow. And it's not even a VPN, It's just a proxy service.
Con Unable to sync extensions
Imagine having 100 extensions and Opera link cannot sync them, which will be troublesome.
Con Basically a Chrome clone
The latest versions of Opera are basically Chrome clones, so they really don't add anything new.
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 No reader view
There is a great reader view extension which is available.
Con No address bar in fullscreen mode
Unlike in Vivaldi.