When I tested on Word through our work account -- the URL of the document is on blahblah-my.sharepoint.com -- on Windows, everything went normally: permission prompt, granted, worked.

Can you confirm that you're allowing sites to prompt for permission? This checkbox on the Options/Preferences page needs to be clear:

If Firefox doesn't prompt, try using the Page Info dialog. While you're on the site, either:

• Ctrl + i (Mac: Command + i)
• (menu bar) Tools > Page Info
• right-click (Mac: Ctrl+click) a blank area of the page > View Page Info

In the Page Info dialog, click the Permissions icon at the top.

On that panel, scroll down to Use the microphone and (A) uncheck Use default and (B) click the permission you want to give the site.

Then you can close this dialog (it saves as you go and there's no save button to click).

Does that work?

The error message also could mean that Firefox itself doesn't have permission to use the microphone, but if it works on other sites, then that shouldn't be the issue.

I can confirm that I'm allowing sites to prompt for permission. The checkbox on the Options/Preferences page is clear.

I have also (A) unchecked Use default and (B) clicked Allow on Use the microphone.

Sadly, it still doesn't work. I get the following error message:

https://user-media-prod-cdn.itsre-sumo.mozilla.net/uploads/images/2020-09-08-16-32-55-492fdf.png

In translation it says:

Problem with dictation There is no access to the microphone. Check that the browser is authorized to use the microphone.

Does your microphone work on the following Mozilla demo page?

https://mdn.github.io/web-dictaphone/

Yes it does. It promts for permission, I chose Allow, and then I can record sound without problem.

Hmm, I'm not sure why Office isn't working. I suspect it's a "cross-site" problem but I'm not sure how to track it down. Perhaps if you check the Web Console on the page it will show that it blocked a cross-site request related to the microphone?

Before triggering the dictation feature, open the Web Console in the lower part of the tab using either:

• "3-bar" menu button > Web Developer > Web Console
• (menu bar) Tools > Web Developer > Web Console
• (Linux and Windows) Ctrl+Shift+k

Then trigger the feature in the upper part of the tab and watch for error or security messages. Anything that sounds like it could be relevant?

I'm not entirely sure if I understand what I'm reading, but there's a lot of output in "Swenglish":

Källmappningsfel: Error: request failed with status 404 Resurs-URL: https://c1-word-edit-15.cdn.office.net/we/s/161330141008_App_Scripts/common.min.js Källmappnings-URL: common.min.js.map

(Källmappningsfel = Source Mapping Error)

It also refers to this link: https://developer.mozilla.org/en-US/docs/Tools/Debugger/Source_map_errors

Next there's another message:

XML-tolkningsfel: syntaxfel Adress: https://word-edit.officeapps.live.com/we/wordeditorframe.aspx?ui=sv-SE&rs=sv-SE&hid=cfnZELicKUGI%2Fo4MIH%2BQcg.0&wopisrc=https%3A%2F%2Fwopi.onedrive.com%2Fwopi%2Ffiles%2FC674A2F9D1106D13!942&wdorigin=OFFICECOM-WEB.MAIN.MRU&wdo=2&wde=docx&sc=host%3D%26qt%3DFolders&mscc=1&wdp=0&uih=OneDrive&jsapi=1&jsapiver=v1Wrapper&newsession=1&corrid=8f7455f1-75b7-4dda-a642-313f7be2c1df&usid=8f7455f1-75b7-4dda-a642-313f7be2c1df&sftc=1&instantedit=1&wopicomplete=1&wdredirectionreason=Unified_SingleFlush Radnummer 1, Kolumn 1:

(tolkningsfel = interpretation error, syntaxfel = syntax error, Radnummer = Row number)

And then a third message:

Uncaught (in promise) Error: SpeechToTextClient was already initialized

This third message is followed by a table with a massive amount of links.

Does any of that make any sense?

Thank you for checking that.

I see when you use the "free" version of Office online for a OneDrive document, it is embedding the editor from a different server (screenshot attached).

Firefox offers a method for sites to transfer microphone permission from the main page to the framed page called Feature Policy. The site adds an allow attribute to the <iframe> tag and Firefox asks the user about permission for the main site and then transfers it to the framed page. I set up a very basic demo and it works:

https://www.jeffersonscher.com/res/featurepolicy.html

The reason I mention all that is Microsoft seems to be trying to use Feature Policy. They have this on their iframe:

allow="microphone https://word-edit.officeapps.live.com; camera https://word-edit.officeapps.live.com;"

That seems right, but it's not working for some reason. Their scripting is complicated so I can't really sort out what they are doing. I might file a bug and see whether someone else can follow it.

I don't understand all the details of your explanation, but I understand enough to realize that this is not a simple problem with a simple solution. For the time being, I will work around the problem by using another browser for this particular task.

I thank you for your efforts in trying to solve this issue!