Hi @Natalie Wilkinson,
The Read aloud feature in Microsoft Edge Chromium are implemented in the Microsoft Voice (Speech Recognition) component/extension. You can enter "edge://components/" in the address bar of Edge and find Speech Recognition to check its update status. In addition, you can also enter "edge://extensions-internals/" in the address bar and search for the key id ("id": "jdiccldimpdaibmpdkjnbmckianbfold") for more information.
As per the current design, the Microsoft Voices (Speech recognition) component/extension is loaded into the Edge frame browser process and requires persistent WebSocket connections to speech.platform.bing.com (on ports 80 and 443) in order to function as expected.
So, the resolution is to allow direct and persistent connections to speech.platform.bing.com for ports 80 and 443.
If read aloud still doesn't work, you can press "Alt+Shift+I" to submit feedback.
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Best regards,
Jinxin Wang