Thanks for the replies. I'm starting to clarify the problem.
I've done the swipe down on Chrome & seen the immediate effect (before the page had changed, so null update).
I tried that on current version of Firefox (v 60.0.2) & a shaded crescent pulls down, like Chrome, though more reluctantly, but it does nothing AFIACT after a page has become out of date.
The 3 dots top right provide a dropdown menu that used to include back (previous page), refresh & forward (next page if back had been used). All 3 of those functions have now disappeared from the menu. I'm guessing that happened with the latest update, but haven't managed to work out when it was installed. It was available 6-Jun, so it presumably "installed itself" between then & 11th, when we went away.
Meanwhile the Windows (10) version of Firefox doesn't have those 3 functions in the equivalent dropdown menu, but neither did the version before 60.0.2 IIRC. I haven't found it an issue with a broadband connection plus keyboard & mouse, but it's a PITA on an Android phone in places with poor internet access.