Mozilla Firefox is a free and open-source web browser developed for Windows, OS X, and Linux, with a mobile version for Android.
Ranked in these QuestionsQuestion Ranking
Pro Strong HTML5 feature support
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 Strong developer tool
The built-in developer tools have been merged with the popular FireBug extension since FF57
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 Awesome customizability
Great library of add-ons
Pro Good font rasterizing
Font rasterizing on Windows is much better than in competitors. Even smaller text is clear and contrast.
Pro Uses less resources
Firefox 57 (Quantum) and newer uses less resources than ever. It is proven with benchmark done by AppleInsider.
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 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.
Pro Automatically updated
Firefox is automatically updated on the platforms where it makes sense.
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 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 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 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 Easy screenshots without extensions
Within the browser itself, you can easily take screenshots and save them to your computer.
Pro Android version allows installation of addons
Unlike other browsers, Mozilla uses almost the same codebase as with the desktop version so extensions work as-is without code modifications - something other browsers cannot do due to their breaking and sometimes unrelated code branches to the mainline desktop branch.
Pro Screenshots tool
Powerful screenshots tool built right into the browser.
Pro Dark theme
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.
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 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 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 GTK on Linux/BSD
This makes the integration on non-GTK Desktop Environments very hard.
Con Some built-in advertising
with their new "pocket" feature, they offer advertisements built-in.
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 No status bar
There's no status bar. Granted, there is a status tool-tip. But what if you want an actual toolbar, you're out of luck.
Con Google obsession
Lately, Firefox has been partnering with Google, leading to some privacy concerns.
Con Poor performance on SSD even without extensions
On a fast SSD such as Corsair Force LE series this browser still performs as if it were installed on a regular hard drive disk, meaning it takes long time to start, even without any extensions. On that matter Google Chrome is light years ahead of Firefox. This applies only for Firefox versions below 60!
Con Can't scroll tabs with mouse wheel
It's pretty basic but you can't switch between tabs back and forth using your mouse wheel. Any add-ons supporting this have been deprecated since FF57.
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 Devtools for WebExtensions are buggy
Con Sometimes buggy
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: https://www.cnet.com/news/mozilla-backpedals-after-mr-robot-firefox-misstep/
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) : https://bugzilla.mozilla.org/show_bug.cgi?id=1406647