tabindex global attribute

- LS

Specifies the focusability of the element and in what order (if any) it should become focused (relative to other elements) when "tabbing" through the document.

IE

  1. 5.5 - 6: Support unknown
  2. 7 - 10: Supported
  3. 11: Supported

Edge

  1. 12 - 79: Supported
  2. 80: Supported

Firefox

  1. 2 - 3.6: Support unknown
  2. 4 - 71: Supported
  3. 72: Supported
  4. 73 - 74: Supported

Chrome

  1. 4 - 14: Support unknown
  2. 15 - 79: Supported
  3. 80: Supported
  4. 81 - 83: Supported

Safari

  1. 3.1 - 5: Support unknown
  2. 5.1 - 12.1: Supported
  3. 13: Supported
  4. TP: Supported

Opera

  1. 9: Support unknown
  2. 9.5 - 65: Supported
  3. 66: Supported

iOS Safari

  1. 3.2 - 13.1: Supported
  2. 13.2: Supported
  3. 13.3: Supported

Opera Mini

  1. all: Support unknown

Android Browser

  1. 2.1 - 4.4.4: Support unknown
  2. 76: Support unknown

Blackberry Browser

  1. 7: Support unknown
  2. 10: Support unknown

Opera Mobile

  1. 10 - 12.1: Support unknown
  2. 46: Support unknown

Chrome for Android

  1. 79: Supported

Firefox for Android

  1. 68: Supported

IE Mobile

  1. 10: Support unknown
  2. 11: Support unknown

UC Browser for Android

  1. 12.12: Support unknown

Samsung Internet

  1. 4 - 9.2: Support unknown
  2. 10.1: Support unknown

QQ Browser

  1. 1.2: Not supported

Baidu Browser

  1. 7.12: Support unknown

KaiOS Browser

  1. 2.5: Supported

Mac OS X "Full Keyboard Access" refers to setting Keyboard→Shortcuts→Full Keyboard Access to "All controls" in the System Preferences.

"Unknown" support for mobile browsers is due to lacking a method of tabbing through fields.

Resources:
MDN Web Docs - tabindex attribute