When comparing Mozilla Firefox vs Sumatra PDF, the Slant community recommends Sumatra PDF for most people. In the question“What are the best PDF viewers for Windows?” Sumatra PDF is ranked 1st while Mozilla Firefox is ranked 8th. The most important reason people chose Sumatra PDF is:
Sumatra is available for free, licensed under GPL with source code available on [GitHub](https://github.com/sumatrapdfreader/sumatrapdf).
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 Syncs between devices
Firefox Sync is an optional feature in Firefox that allows syncing bookmarks, passwords, and add-ons between devices.
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 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.
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 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 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 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 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 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 A lot of add-ons
An enormous number of add-ons.
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 Really independent browser
It's not dependent on Google.
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 Built-in privacy protection
Blocks tracking cookies, finger print scanners and Cryptominers by default. Can be changed to the user's individual needs.
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 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!
Pro Very secure
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 Installed by default on many Linux distributions
Many Linux distributions come preinstalled with Mozilla Firefox
Firefox has a solid mobile app.
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.
Master about:config and uBlock Origin, and all Firefox-based browsers will be yours.
UI is better than any other chromium-based browser.
Pro Free and open source
Sumatra is available for free, licensed under GPL with source code available on GitHub.
Pro Starts quickly
Pro Low resource usage
Pro Elegant interface
Pro Does not have heavy editor features
Annotations and other heavy features are just not needed in reader.
The application consists of a single file that can be run without installation. You can put it on an external device, such as an usb thumb stick and run it on any Windows machine from the thumb stick.
Pro Extensive keyboard shortcuts
It's available in 69 languages.
Con Some built-in advertising
With their new "pocket" feature, they offer advertisements built-in.
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 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 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 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 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 Doesn’t support multiple languages for spell check
If you write in multiple languages, you need to manually switch the spell check language.
Con Antivirus has False positives
All Downloads in Firefox are scanned for viruses, but there are a lot of false positives.
Con Terrible user interface
Con Crappy license
Cannot redistribute binary after source code modification.
Con New icon looks ugly
Con Major updates may break any installed add-ons
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 Now forces install and use of snap
Only on Ubuntu
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 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 Lacking in features
Sumatra aims for simplicity at the expense of functionality. For example, there's no way to annotate PDFs or edit them.
Con Windows only
Con Fonts are not smooth enough
Not as smooth as e.g. Adobe Reader. No anti-aliasing
Con Cannot crop empty fields
Just got used to this killing feature on Goodreader on Mac.