The menu bars (eg 'File', 'Edit', 'View' etc) and the various buttons in the Fireworks UI are extremely small. Normally this would suggest that my screen resolution is wrong, but it's right for other applications such as Chrome, Word and so on. Is there a way to make the UI bigger?
No - you are working on a retina high resolution screen, and Fireworks does not support that. Nor will it ever, since Adobe stopped development and support since 2013.
If you are on a mac, you can force FW to start up in low resolution (Get Info-->Open in Low Resolution). That will open FW with larger, fuzzy looking, icons.
If you work on a Windows machine, you are out of luck. Or change the screen resolution to a twice lower one (which defeats the purpose of your nice high-res screen).
OK, many thanks for the info.