On the standards track: Yes
Is Experimental: No
Is Deprecated: No
In Chrome version 4 on 2010-01-25 Note: This property is only supported on Windows and Linux. Initial versions had bugs on Windows and Linux that broke font substitution, small-caps, letter-spacing or caused text to overlap. See bug 40156511, bug 40430936, bug 40444347, bug 40286561.
In Chrome Android version 18 on 2012-06-27 Note: This property is only supported on Windows and Linux. Initial versions had bugs on Windows and Linux that broke font substitution, small-caps, letter-spacing or caused text to overlap. See bug 40156511, bug 40430936, bug 40444347, bug 40286561.
In Edge version 79 on 2020-01-15 Note: This property is only supported on Windows and Linux. Initial versions had bugs on Windows and Linux that broke font substitution, small-caps, letter-spacing or caused text to overlap. See bug 40156511, bug 40430936, bug 40444347, bug 40286561.
In Firefox version 1 on 2004-11-09 Note: This property is only supported on Windows and Linux. The optimizeSpeed option has no effect on Firefox 4 because the standard code for text rendering is already fast and there is not a faster code path at this time. See bug 595688 for details.
In Firefox for Android version 46 on 2016-04-26
Not in Internet Explorer
In Quest Browser version 5.0 on undefined Note: This property is only supported on Windows and Linux. Initial versions had bugs on Windows and Linux that broke font substitution, small-caps, letter-spacing or caused text to overlap. See bug 40156511, bug 40430936, bug 40444347, bug 40286561.
In Opera version 15 on 2013-07-02
In Opera Android version 14 on 2013-05-21
In Safari version 5 on 2010-06-07
In Safari on iOS version 4.2 on 2010-11-22
In Samsung Internet version 1.0 on 2013-04-27 Note: This property is only supported on Windows and Linux. Samsung Internet is not on Windows or Linux.
In WebView Android version 3 on 2011-02-22 Note: From version 3 to 4.3, there is a serious bug where text-rendering: optimizeLegibility causes custom web fonts to not render. This was fixed in version 4.4.
In WebView on iOS version 4.2 on 2010-11-22