Oracle developer Forms version 10g is still used. Used by Oracle for their E-Business Suite & they will continue using this obsolete, unstable version until the day EBS is discontinued. So, let us see how to make the best out of what is available.
One of the major nuisances a developer (definitely) will come across while using this obsolete version of Oracle Developer on Windows 7 or later versions of Microsoft OS is, opening a module that has underlying database level objects changed (procedures/functions/packages), this IDE crashes without generating any error logs. Simple as it is. This could completely cripple the developer, especially when rapid developments miss to document the changes.
Is it possible to open FMB files without being connected to database? it is another BIG NO NO. Developer 10G will crash immediately incase if you try to open an FMB file that has database objects referred. So what is the next possible solution?
Well there is a solution that is dirty, having to install Oracle Forms Developer 12c (12.2.1.4). Just install the suite as standalone without Weblogic. This version is fault tolerant and will not try to validate the database level object calls & crash. By this, you can verify, compile and see what objects were changed, non-existing etcetera.

Oh yes, make sure you have copied your source FMB files to a new folder prior opening them with Forms Developer 12c!. Always remember, Oracle EBS R12 only compiles FMB files created using Oracle forms 10g. You could lose your original files forever if you forgot to do that.
Here is an excellent article explains how to install standalone Oracle Forms 12c.
https://oracle-base.com/articles/12c/standalone-forms-builder-12c-installation-on-windows-1221