outlook.com: Text selection get undone when trying to change font because of Safari sniffing in rooster

[karlcow]

This is happening when using the top and contextual menu for changing font in Outlook mail.

Office uses Microsoft's rich text editor, roosterjs, which sniffs for Safari and has it's own selection logic.
The WebKit fixed it partially by sending a Chrome UA string.

The bug persists with jus the chrome UA string.
roosterjs has it's own selection logic for Safari.
a change has been made in the FocusController to preserve selection when focus leaves a contentEditable root to a non-editable target.
WebKit/WebKit#61173
https://bugs.webkit.org/show_bug.cgi?id=310549
We would like very much to avoid to have to quirk, but in the current circumstances this is the only solution to help our common customers.

Steps to reproduce the behavior:

1. Go to outlook.com - login with test account
2. Create New Email, type some text in the body - e.g. this is text
3. Highlight text to apply formatting (more than one)
4. Start with Font and once you apply font, try to do size change or anything else - selection is gone.

Expected behavior
Selection should stay on selected text so multiple formatting can be applied.

Device Information

• OS: iPad
• Browser Safari
• Version 18.6.2 and 26.0 and future versions.

This creates a webcompat issue for Safari. @captainbrosset fyi.