Can I use
?

Filesystem & FileWriter API

- UNOFF

Method of reading and writing files to a sandboxed file system.

Chrome

  1. ❌ 4 - 7: Not supported
  2. ◐ 8 - 12: Partial support
  3. ✅ 13 - 135: Supported
  4. ✅ 136: Supported
  5. ✅ 137 - 139: Supported

Edge

  1. ❌ 12 - 18: Not supported
  2. ✅ 79 - 135: Supported
  3. ✅ 136: Supported

Safari

  1. ❌ 3.1 - 18.4: Not supported
  2. ❌ 18.5: Not supported
  3. ❌ TP: Not supported

Firefox

  1. ❌ 2 - 137: Not supported
  2. ❌ 138: Not supported
  3. ❌ 139 - 141: Not supported

Opera

  1. ❌ 9 - 12.1: Not supported
  2. ✅ 15 - 116: Supported
  3. ✅ 117: Supported

IE

  1. ❌ 5.5 - 10: Not supported
  2. ❌ 11: Not supported

Chrome for Android

  1. ✅ 136: Supported

Safari on iOS

  1. ❌ 3.2 - 18.4: Not supported
  2. ❌ 18.5: Not supported

Samsung Internet

  1. ❌ 4: Not supported
  2. ✅ 5 - 26: Supported
  3. ✅ 27: Supported

Opera Mini

  1. ❌ all: Not supported

Opera Mobile

  1. ❌ 10 - 12.1: Not supported
  2. ✅ 80: Supported

UC Browser for Android

  1. ✅ 15.5: Supported

Android Browser

  1. ❌ 2.1 - 4.4.4: Not supported
  2. ❌ 136: Not supported

Firefox for Android

  1. ❌ 137: Not supported

QQ Browser

  1. ❌ 14.9: Not supported

Baidu Browser

  1. ✅ 13.52: Supported

KaiOS Browser

  1. ❌ 2.5: Not supported
  2. ❌ 3: Not supported

The File API: Directories and System specification is no longer being maintained and support may be dropped in future versions.

Resources:
Firefox tracking bug
WebPlatform Docs
HTML5 Rocks tutorial