So I now decided it would be nice to install firefly iii.
This needs Composer.
So installing Composer is proving harder than expected.
The download keeps timing out go gave up and just downloaded latest version (1.6.5) from here
https://getcomposer.org/download/
Created a /usr/local/composer directory and downloaded the file into that.
Then executed
mv /usr/local/composer/composer.phar /usr/local/bin/composer chmod +x /usr/local/bin/composer composer -v
All seems OK now
The problem seems to be something to do with the way curl works with ipv6 vs ipv4.
I also enabled ipv6 on the OMV box.
So I did add
ipv4 >> ~/.curlrc
but still made no difference.