You can easily transfer Mac OLM files to Mozilla Thunderbird using MacUncle OLM to Thunderbird Converter. The tool supports Mac OS Machines.
Start OLM to Thunderbird Converter mac and add OLM file to the software panel using either Add File(s) or Add Folder(s).
Choose Thunderbird option and you can also select destination path if required and press the Export button to start the conversion process.