| Microsoft Edge
You'll actually need to install this before you can install any mTurk related userscripts. Userscripts are by far the most powerful tool in increasing your mTurk earnings as they allow heavy modification of many HITs as well as offer improvements to the standard mTurk interface and worker experience.
This currently in-development browser extension by @Kadauchi
seeks to replace and consolidate many userscripts that Turkers find most effective in their daily workflow.
An auto-refreshing extension is always good to have installed for times when userscripts don't fit the bill.
This lets you quickly organize and move tabs around multiple screens.
Quickly split Chrome in half, allowing you to auto-open links in the 2nd window. This is great for HITs requiring you to visit an outside website.
Don't Track Me Google
Allows you to easily copy website links directly from Google
results without all the extra garbage. Very useful for a multitude of data research HITs.
During the day, computer screens look good—they're designed to look like the sun. But, at 9PM, 10PM, or 3AM, you probably shouldn't be looking at the sun.
f.lux fixes this: it makes the color of your computer's display adapt to the time of day, warm at night and like sunlight during the day.
Google VoiceGoogle Voice is great for HITs which require making phone calls. Accounts are free for US calls and provide a way to avoid having contacted #s seeing your personal cell #.
Synergy is a program that allows you to control multiple computers through one keyboard/mouse combo. It provides a more seamless experience than Remote Desktop Software for computers that are close together and setups where the monitors for multiple computers are in view from the same place.
Synergy works across OS (Windows, Linux, Mac).
Mouse Without BordersMouse Without Borders Website
MWB is similar to Synergy but will only work across Windows OS.