Comment 5 for bug 1375889

Testing with silo 68 which contains the UA override.
I first delete any cache files in .local/share/webbrowser-app and gmail webapp, then launch the browser or gmail webapp.

The override works most of the time (you can tell if you see the black "Updated" footer on the main gmail screen when press the refresh button, or when replying to a mail if the original message is formatted correctly.)

Try to close the app and restart it. Do this multiple times and frequently gmail is rendered without the override as you don't see the footer and reply messages are not formatted.