According to Can I use, as of June 2017, 93.75% of Internet usage is on a browser that supports unprefixed linear gradients (97.2% in the US). For most people, this means you don't need to prefix your gradients anymore.
Below is the first compatible version and release date for the most common desktop browsers:
- IE v10, released September 2012
- Firefox v16, released August 2012
- Chrome v26, released February 2013
- Safari v6.1, released October 2013
- Opera 12.1, released November 2012
Information on compatibility history of other browsers (including mobile browsers) is available at Can I use.
