Is it Firefox version 66.0, 66.0.1 or 66.0.2?

Just updated it to 66.0.2 (64 bit) and tested, still doing it.

Microsoft's scripts require a legacy behavior, and Firefox has a preference where you can list servers that can't handle the new behavior. Firefox 66.0.2 was supposed to update that list, but it sounds as though you might need to do it by hand. Here's how:

(0) Select and copy this list:

*.collabserv.com,*.gov.online.office365.us,*.officeapps-df.live.com,*.officeapps.live.com,*.online.office.de,*.partner.officewebapps.cn,*.scniris.com

(1) In a new tab, type about:config in the address bar and press Enter/Return. Click the button accepting the risk.

(2) In the search box above the list, type or paste hack and pause while the list is filtered

(3) Double-click the dom.keyboardevent.keypress.hack.use_legacy_keycode_and_charcode preference to pop up a small dialog.

• If the box is blank, paste the new list an click OK.

• If there is an existing value other than the list above, add a command, then paste the new list and click OK.

That will take effect in your Word editor the next time you reload the page. You may want to use Ctrl+Shift+r to reload fully, bypassing cached files.

If that doesn't work:

What is the address of the editing frame? To check on that, right-click the document, expand This Frame, then click View Frame Info.

For comparison, mine is:

https://word-edit.officeapps.live.com/we/wordeditorframe.aspx

So it is covered by *.officeapps.live.com in that list.

For what it's worth, my automatic update didn't insert that list, but exiting Firefox and starting it up again updated it. Much easier than my earlier suggestion!

Thank you! I should have known it would be a variation of "Turn it off and back on again"!