Can I use
?

MPEG-4/H.264 video format

- OTHER

Commonly used video compression format.

IE

  1. 5.5 - 8: Not supported
  2. 9 - 10: Supported
  3. 11: Supported

Edge

  1. 12 - 84: Supported
  2. 85: Supported

Firefox

  1. 2 - 20: Not supported
  2. 21 - 34: Partial support
  3. 35 - 79: Supported
  4. 80: Supported
  5. 81 - 82: Supported

Chrome

  1. 4 - 84: Supported
  2. 85: Supported
  3. 86 - 88: Supported

Safari

  1. 3.1: Not supported
  2. 3.2 - 13.1: Supported
  3. 14: Supported
  4. TP: Supported

Opera

  1. 9 - 24: Not supported
  2. 25 - 69: Supported
  3. 70: Supported

iOS Safari

  1. 3.2 - 13.7: Supported
  2. 14.0: Supported

Opera Mini

  1. all: Not supported

Android Browser

  1. 2.1 - 2.2: Partial support
  2. 2.3: Partial support
  3. 3 - 4.3: Partial support
  4. 4.4 - 4.4.4: Supported
  5. 81: Supported

Blackberry Browser

  1. 7: Supported
  2. 10: Supported

Opera Mobile

  1. 10: Not supported
  2. 11 - 12.1: Supported
  3. 46: Supported

Chrome for Android

  1. 85: Supported

Firefox for Android

  1. 79: Partial support

IE Mobile

  1. 10: Supported
  2. 11: Supported

UC Browser for Android

  1. 12.12: Partial support

Samsung Internet

  1. 4 - 11.2: Supported
  2. 12.0: Supported

QQ Browser

  1. 10.4: Supported

Baidu Browser

  1. 7.12: Supported

KaiOS Browser

  1. 2.5: Supported

Firefox supports H.264 on Windows 7 and later since version 21. Firefox supports H.264 on Linux since version 26 if the appropriate gstreamer plug-ins are installed.

Partial support for older Firefox versions refers to the lack of support in OS X & some non-Android Linux platforms.

Resources:
Firefox extension allowing support in Win7
Wikipedia article