I have now put in place a solution which means that the entire contents of a given formula should be visible in all cases, i.e. those contents do not extend off the edge of the screen. This should have fixed the issue not only in Google Chrome, but hopefully also in Firefox.
The resulting formatting is not quite as I would have wished, though it at least means that posts are no longer rendered unreadable.
I would just like to add a belated thanks to Vaibhav, whose suggestion many months ago has proved to be extremely useful. So thank you, Vaibhav, and sincere apologies for not having resolved this issue for my Firefox readers until now.