Recs.
Updated
Vivaldi is a Chromium based browser with its UI written with web technologies (HTML/JS). Vivaldi advertises itself as a "power-user browser" as it tries to bring features built-in reducing the number of extensions needed.
Vivaldi was founded by Jón S. von Tetzchner, creator of Opera browser and its CEO until before the switch to Chromium.
SpecsUpdate
Pros
Pro Compatible with all Chrome extensions
Since Vivaldi is built on Chromium, the same base as Chrome (among other browsers) is built on, it was possible for Vivaldi developers to allow Chrome extensions to run in their browser.
Pro Lots of features and customizability
Vivaldi has a lot of features and customizability. Far more then most (perhaps all) other browses, and many to list them all individuality as separate pros.
Pro Notes
A notes panel allows to save notes from webpages and can include screenshots for reference and have tags and organized in folders to help manage them. Thumbnails are too small and Notes do not have separate page in settings, but it should, there are a lot of things to improve.
Pro Custom search engines
You can add as many search engines as you like. For example you can set up one for YouTube, one for Wikipedia, or whatever you want: you need only the URL of the search and it can be used from the URL bar (by prefixing it's nickname, yt
for YouTube for example).
Pro Tab behaviour can be customised
The order you toggle, open, close or clone tabs can be modified to match a workflow that best works for you. For example you can choose tabs to toggle in recent order so you can go back and forth between the last most useful tabs without needing to change their position on the tab bar.
Pro Manages bookmarks well
Vivaldi has an excellent bookmarks system. Bookmarks can be easily accessible via Speed Dial, side-bar, bookmarks bar, quick commands. No more messy bookmarks bar is needed and location bar suggestion is improved thus!
Pro Built-in page capture
Vivaldi can grab a picture of the whole webpage or part of it and saves it automatically inside a note or as a file in your disk, or in your elected directory. But I have problems with images of full windows shown on monitor (using X Window System in GNU/Linux). Here I use system XWindow screenshots.
Pro Programmable user interface
For you programmers out there: Since Vivaldi uses JavaScript, React, Node.js, Browserify and multiple npm packages to build the browser, it can be customized with ease by anyone who knows HTML, CSS, and JavaScript.
Pro Built-in ad and tracker blocker
Vivaldi has a built-in blocker that allows you to select between blocking just trackers or both trackers and ads. With customizable blocking list sources, good performance, and support for all the standard blocker list features you find in ad blocker extensions (with more to come), you might not need an ad blocker extension at all.
This also comes in handy on Android, where Chromium/Vivaldi doesn't support extensions.
Pro Updates via dialog box
Unlike most modern browsers (but like most browsers of yesteryear), Vivaldi gives you a dialog box when an new version comes out; it doesn't just update silently in the background. The dialog box tells you about the changes that have been made, and lets you chose when you want to update.
Pro Customizable UI Theme and colors
Vivaldi can change the colors across the browser and has the option to change the color automatically depending on the page. Also, page loading animations are available in the address bar.
Pro Side panel and status bar
Unlike most modern browsers (but like most browsers of yesteryear), Vivaldi has a status bar. But the status bar is optional, you can turn it off (in the settings) if you don't want it. Vivaldi also has a side-panel, which again, can be turned off.
Cons
Con Some non-optional telemetry
According to its privacy policy, Vivaldi sends an approximate location (country or major city), randomized ID, version, cpu architecture, screen resolution (to know what screen sizes to test on) and time since last message every 24 hours (to know amount of active users).
Con Sponsored bookmarks
Vivaldi has a number of preinstalled bookmarks, like Amazon. On some occasions, new bookmarks have been added when the browser updates. All of these bookmarks can be deleted, same as any other bookmark.
Con Can't disable all telemetry
Vivaldi needs some amount of knowledge about the amount of active users, for business deals.
Con Same security vulnerabilities as Chrome
Vivaldi uses the same browser engine as Chrome, meaning it has the same security-vulnerabilities as Chrome. Chrome is a big target for hackers (being the most popular browser in the world), and a vulnerability for Chrome will likely also exist in Vivaldi.
Con No automatic silent background updates, except on macOS
Unlike most modern browsers, Vivaldi doesn't have the option to update silently in the background. It gives you a dialog box when an update comes out. The box doesn't warn you that not updating the browser could expose you to security risks, which could be pretty bad for your average joe, who doesn't know computers that well.
Con No option to open saved tab stack as a tab stack
You may save stack, but you can open it as separate tabs. Interesting that when you save session with stacks, you'll be able to open the stacks with inner settings of page tiling (size and zoom) as well. Contradiction worth of shame.
Con Partially proprietary
While Vivaldi is currently available gratis (without monetary charge), it is currently not fully libre (meaning that it does not allow users to view the source code used to create, to modify that code, or to redistribute modifications).
It is therefore not considered free or open-source software.
The C++ source code, for the Chromium backedn, however is open-source under a BSD license and can be downloaded and browsed from here.
The UI code is not open-source, but consists of easily readable HTML, CSS & JS. Modifications can be shared on their forum's dedicated section.
Con Some users seem to believe the developers do not care for your privacy
Con No built-in proxy
Unlike Opera Proxy (which leaks your IP address), Vivaldi doesn't have a proxy service out of the box. You'll need an extension or an external program, to use Vivaldi with a proxy server.
Recommendations
Comments
Flagged Pros + Cons
Pro Cross browser extensions with Opera and Chrome, Firefox web-ext's too
All Vivaldi, Opera and Chrome users can get extensions from all extension/addon sites, especially from Opera Addons and Chrome Store.
Pro VPN is available by extension- also routing through Tor network
VPN and Tor encryption is possible through extensions. Tor is a free choice if one doesn't want to subscribe to a VPN service.
Pro Pioneer of browser features
Presto Opera (Vivaldi's predecessor) is the reason we have a number of common browser features, including tabs and speed dial.
Pro uBlock Origin and uMatrix for privacy and ad blocking
The best privacy and ad blocking extensions are available.
Pro Custom keyboard shortcuts
You can change and add keyboard shortcuts for basically all commands. It also has single key shortcuts to execute actions with one click.
Con Always regressing with every update
With every update the devs release they regress something. You just get accustomed to a feature and in the next update it's being removed without even asking you whether you want it to be removed. They tend to remove more features than they add.
Out of Date Pros + Cons
Con Not available on iOS/iPadOS
There is an Android version of Vivaldi, but no iOS/iPadOS version yet. iPhone and iPad users are out of luck for the time being.
Con Small chance you will lose your session
In rare circumstances, the browser window may freeze. Sometimes you then lose all your progress, open windows, and session without an option to restore it next time you open your browser.
Con No automatic page translation
Unlike Chrome, it doesn't automatically translate pages that are not in your language, since this requires service integrations Vivaldi can't afford to buy access to.
Con Extensions miss hotkeys
You can set your shortcuts at vivaldi://extensions, but they do not work.
Con No built-in adblocker
Unlike Opera (but like most browsers), Vivaldi doesn't have an adblocker out of the box. You'll need an extension, if you want Vivaldi to block ads.
Con New and buggy
Still working out a few kinks, not entirely optimized yet so it can be a little slow or resource intensive. The latest versions have much improved performance though.
Con Developer Tools does not embed
When you attempt to Inspect Element on a webpage, the Developer Tools pane opens in a new window and cannot be attached to the right or the bottom of the current page. However, this can be solved with 3rd-party JavaScript hooks.