IOS Version 1130-k9w7-mx.124-10b.JA needed Internet Explorer version 6 for web configuration.
I obtained an AP-1242AG with a later IOS version 1240-k9w7-mx.124-21a.JA1. Checking the release notes for this version revealed that Firefox browser was now supported.
I then obtained a copy of 1130-k9w7-mx.124-21A.JA1 to upgrade my 1130.
Firstly I backed up the existing IOS to my tftp server using a console connection:
#archive upload-sw tftp://192.168.1.1/c1130-k9w7-mx.124-10b.JA.tar
Then I uploaded the new IOS to the AP:
#archive download-sw /overwrite tftp://192.168.1.1/c1130-k9w7-tar.124-21a.JA1
Next a reload and a show version to verify the correct version.
And finally, check the browser interface with Firefox.