Read-only depends on the Security settings and if it has been assigned the fmiwp Extended Privilege.
FMServer is recommended, not merely FMP for use with IWP.
Remember that FM11 is no longer supported by FMI after Sept 25, 2015:
Just keep in mind that IWP is only an approximation of your layouts
It may take a bit of work to get it presented properly in a Browser
> I should activate Instant web publishing for each and any file