I've had to change my default text/html .html handler from a text editor to a browser to support the opening sequence of git annex webapp. any other way around this? perhaps to have it open the page in the default browser rather than the default text/html handler?
Not without exposing the secret token to other users in the system by passing it as a parameter to the browser command. Which is why it uses the method it does.
But, you can configure it to use a specific browser in the standard git way:
git config web.browser chromium