Opus

Royalty-free open audio codec by IETF, which incorporated SILK from Skype and CELT from Xiph.org, to serve higher sound quality and lower latency at the same bitrate.

IE

5.5 - 10: Not supported
11: Not supported

Edge

12 - 13: Not supported
14 - 91: Supported
92: Supported

Firefox

2 - 14: Not supported
15 - 89: Supported
90: Supported
91 - 92: Supported

Chrome

4 - 32: Not supported
33 - 91: Supported
92: Supported
93 - 95: Supported

Safari

3.1 - 10.1: Not supported
11 - 14: Partial support
14.1: Partial support
15 - TP: Partial support

Opera

9 - 19: Not supported
20 - 76: Supported
77: Supported

Safari on iOS

3.2 - 10.3: Not supported
11 - 14.4: Partial support
14.5: Partial support

Opera Mini

all: Not supported

Android Browser

2.1 - 4.4.4: Not supported
92: Supported

Opera Mobile

10 - 12.1: Not supported
64: Supported

Chrome for Android

92: Supported

Firefox for Android

90: Supported

UC Browser for Android

12.12: Supported

Samsung Internet

4: Not supported
5 - 13.0: Supported
14.0: Supported

QQ Browser

10.4: Supported

Baidu Browser

7.12: Supported

KaiOS Browser

2.5: Supported

Support refers to this format's use in the audio element, not other conditions.

For Opera the Linux version may be able to play it when the GStreamer module is up to date and the served mime-type is 'audio/ogg'.

Resources:: Google's statement about the use of VP8 and Opus codec for WebRTC standard; Introduction of Opus by Mozilla; Microsoft Edge feature request on UserVoice