Can I use
?

MPEG-4/H.264 video format

- OTHER

Commonly used video compression format.

Chrome

  1. 4 - 118: Supported
  2. 119: Supported
  3. 120 - 122: Supported

Edge

  1. 12 - 118: Supported
  2. 119: Supported

Safari

  1. 3.1: Not supported
  2. 3.2 - 17.0: Supported
  3. 17.1: Supported
  4. 17.2 - TP: Supported

Firefox

  1. 2 - 20: Not supported
  2. 21 - 34: Partial support
  3. 35 - 119: Supported
  4. 120: Supported
  5. 121 - 123: Supported

Opera

  1. 9 - 24: Not supported
  2. 25 - 103: Supported
  3. 104: Supported

IE

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

Chrome for Android

  1. 119: Supported

Safari on iOS

  1. 3.2 - 17.0: Supported
  2. 17.1: Supported
  3. 17.2: Supported

Samsung Internet

  1. 4 - 22: Supported
  2. 23: Supported

Opera Mini

  1. all: Not supported

Opera Mobile

  1. 10: Not supported
  2. 11 - 12.1: Supported
  3. 73: Supported

UC Browser for Android

  1. 15.5: 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. 119: Supported

Firefox for Android

  1. 119: Partial support

QQ Browser

  1. 13.1: Supported

Baidu Browser

  1. 13.18: Supported

KaiOS Browser

  1. 2.5: Supported
  2. 3: 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