display: run-in

- WD

If the run-in box contains a block box, same as block. If a block box follows the run-in box, the run-in box becomes the first inline box of the block box. If an inline box follows, the run-in box becomes a block box.

IE

  1. 5.5 - 7: Not supported
  2. 8 - 10: Supported
  3. 11: Supported

Edge

  1. 12 - 79: Not supported
  2. 80: Not supported

Firefox

  1. 2 - 72: Not supported
  2. 73: Not supported
  3. 74 - 75: Not supported

Chrome

  1. 4 - 31: Supported
  2. 32 - 79: Not supported
  3. 80: Not supported
  4. 81 - 83: Not supported

Safari

  1. 3.1 - 4: Supported
  2. 5 - 6: Supported
  3. 6.1: Support unknown
  4. 7 - 12.1: Not supported
  5. 13: Not supported
  6. TP: Not supported

Opera

  1. 9 - 18: Supported
  2. 19 - 65: Not supported
  3. 66: Not supported

iOS Safari

  1. 3.2: Supported
  2. 4 - 7.1: Supported
  3. 8 - 13.1: Not supported
  4. 13.2: Not supported
  5. 13.3: Not supported

Opera Mini

  1. all: Supported

Android Browser

  1. 2.1 - 4.4: Supported
  2. 4.4.3: Not supported
  3. 80: Not supported

Blackberry Browser

  1. 7: Supported
  2. 10: Supported

Opera Mobile

  1. 10 - 12.1: Supported
  2. 46: Not supported

Chrome for Android

  1. 80: Not supported

Firefox for Android

  1. 68: Not supported

IE Mobile

  1. 10: Supported
  2. 11: Supported

UC Browser for Android

  1. 12.12: Not supported

Samsung Internet

  1. 4 - 9.2: Not supported
  2. 10.1: Not supported

QQ Browser

  1. 1.2: Not supported

Baidu Browser

  1. 7.12: Not supported

KaiOS Browser

  1. 2.5: Not supported
Resources:
Mozilla bug report
CSS Tricks article