1. Security Plugins

Learn about installing extensions in a browser, and preventing security and/or privacy risks:

• Exclusive: Massive spying on users of Google's Chrome shows new security weakness | Reuters
• These 19 Nordstrom Anniversary Sale Beauty Items Are Selling Fast
• How safe are browser extensions? Things you need to know | Kaspersky official blog
• How to Make Sure Your Browser Extensions Are Safe | WIRED

 2. Valuable Extensions That Are Not Often Mentioned

• PerfectPixel by WellDoneCode (pixel perfect) - Chrome Web Store - Useful for web designers who have to convert a design from a PhotoShop graphic to a live & working website. It overlaps a transparent image with the design to the actual website, so, if necessary, one can make adjustments to make the live website look exactly like the design graphics.
• Imagus - Chrome Web Store - If you hover over an image, this extension will make that image larger. 
• TunnelBear VPN - Chrome Web Store - Use this extension to get a different IP address, from a country of your choice. You do have a free limit of (currently) 500 MBs / month, but for occasional visits, this works fine.
• Copy All Urls - Chrome Web Store - When we created this article, we worked with lots of tabs at the same time. In the end, we wanted to copy all the URLs, for all tabs and put them in the document to publish. This extension (there are more who do similar things) helped us do that.
• Export Tabs - Chrome Web Store - This extension offers the opposite solution to the one above - if you have a list of 10 URLs, this extension makes it easy to open all of them at once. Useful for working with lots of tabs at once.
• Absolute Enable Right Click & Copy - Chrome Web Store - Some websites block copy & pasting, while others disable the right-click menu. This extension allows setting them back.
• Sexy Undo Close Tab - Chrome Web Store - It's surprising to see how few people use this extension. If you open and close 10 tabs, and want to open back one of the recently closed tabs, you do have some options in Chrome, like viewing history or pressing a shortcut (Ctrl + Shift + T / Command + Shift + T) multiple times. But this extension, by allowing you to see a list of closed tabs, makes it so much easier.
• I don't care about cookies - Chrome Web Store - If you always hit "Accept all" on cookie messages, and prefer to see them less often; try this extension. It automatically accepts all cookies. Do note that for some websites, there might be errors, so you'll need to disable it accordingly.
• ColorZilla - Chrome Web Store - If you need a Colorpicker (to get the HTML code of color) on a page, this site helps you with that.
• View Image Info (properties) - Chrome Web Store - This extension makes it easy to see basic information about an image, like resolution (width x height) or file size (in MB or KB).
• Open Selected Links - Chrome Web Store - This extension allows you to select a text and open all the links within that area.
• Backspace to go Back - Chrome Web Store - If you want to use the Backspace key on the keyboard to go back a page, this extension will help you do so.
• Bitly | Powerful Short Links - Chrome Web Store - For shortening URLs and getting traffic details - if you share a link on social media, and you want to see how many people click on the link, you can use this extension. Do note that some statistics about the links are available for anyone to see.

3. Extensions That Are Frequently Mentioned

• MozBar - Chrome Web Store - Gives you useful information for SEO purposes, like on-page data or information about backlinks. Lots of SEOs use this.
• SEOquake - Chrome Web Store - SEO metrics for SEO, keyword difficulty, on-page audit, link data. Again, widely used among SEOs.
• Check My Links - Chrome Web Store - Useful to easily find broken links within a page (for SEO purposes). So, if a page links to 20 different other pages, you can easily see, using this extension, if there are some not functional links.
• User-Agent Switcher - Chrome Web Store - a bit technical, a useful extension for SEOs who want to imitate other browsers, devices, or search engine spiders. If you want to "mimic" another spider, this extension will help.
• Evernote Web Clipper - Chrome Web Store - If you want to save some of the things that spark your interest while browsing the web. The Internet can be fragile - you read something today, and perhaps later it won't be online, or you won't remember the details to find it again. With a tool like this, you can save data for later use.
• Save to Pocket - Chrome Web Store - If you find an article you like, but you prefer to read it later, Pocket can help.
• Send to Kindle for Google Chrome - Chrome Web Store - The name says it all. Useful for reading large articles on a Kindle.
• RSS Feed Reader - Chrome Web Store - If you prefer to subscribe to websites using RSS (details on what RSS is). The free version should be good enough for a lot of users.
• Awesome Screenshot & Screen Recorder - Chrome Web Store - For taking screenshots (save a website as an image) and video recordings of the screen.
• GoFullPage - Full Page Screen Capture - Chrome Web Store - For taking screenshots. Use the keyboard shortcut for faster results.
• Screencastify - Screen Video Recorder - Chrome Web Store - Mostly focused on video recordings of the screen. Screencasts can prove to be an efficient way to explain something to another user.
• The Camelizer - Chrome Web Store - Find out the historical data of prices on Amazon.com and other International versions. It can help you know how the current price compares with historical data.
• svg-grabber - get all the svg's from a site - Chrome Web Store - For saving certain types of images. SVGs are graphic-format images. If you often find yourself in the need of saving such files (logos, for example), this extension can help. 
• Fonts Ninja - Chrome Web Store - For web designers, to easily find out more things about a font a site is using. 
• Window Resizer - Chrome Web Store - Testing a website on various resolutions. It’s more than just resizing the browser window– if you're a web designer/web developer and are often faced with the need to test a website at different resolutions, this extension is for you.
• TinEye Reverse Image Search - Chrome Web Store - Useful for web designers who want to find the source of an image.
• Search by Image - Chrome Web Store - Similar functionality to the add-on above.
• Unshorten.link - Chrome Web Store - the opposite of Bit.Ly. If someone sends you a bit.ly (for example) link, and you want to see what's "behind" that link.
• Any.do Extension - Chrome Web Store - Task manager (for productivity purposes). A very popular extension.
• Todoist for Chrome - Chrome Web Store - Task manager (for productivity purposes). 
• Strict Workflow - Chrome Web Store - For productivity, a solution based on the Pomodoro technique - 25 minutes of work, balanced with a 5-minute break afterward.
• StayFocusd - Chrome Web Store - An extension with similar functionality to the one above, blocking access to some websites. It does not use the Pomodoro timer.
• LastPass: Free Password Manager - Chrome Web Store - A very popular password manager. You can't have both the desktop/mobile versions for free, just one. It helps a lot with security.
• Dashlane - Password Manager - Chrome Web Store - A password manager and a form filler.
• Grammarly for Chrome - Chrome Web Store - Spellcheck. The free version gives you plenty of value.
• Buffer - Chrome Web Store - For easy sharing on social media. If you use a lot of accounts at the same time, this can be a lifesaver.

Additional Extensions

• 25 Best Google Chrome Extensions You Need to Use In 2021
• The 15 Best Chrome Extensions to Install Right Now
• Best Google Chrome Extensions of 2020 | Tom's Guide
• The 50 Best Chrome Extensions for Entrepreneurs to Get in 2021
• The Best Free Google Chrome Extensions | PCMag
• The 44 Best Chrome Extensions for 2021

While the extensions mentioned in this article will be most relevant for individuals working in the online field - digital marketing, specifically; this valuable resource will help any user choose the right extension for various scenarios.