Hi   !
Click on the bookmarks icon   (next to the star), then click on 'Show All Bookmarks' (at the bottom of the dropdown), which will take you to the Library. Click on 'Import and Backup', then click on 'Import Data from Another Browser' => click on Internet Explorer.

I'm not sure Firefox for Mac will "import from IE" if it doesn't find IE installed -- not that I recommend trying to do that, since any IE for Mac is ancient and most likely won't even work.

On Windows, you could read them with IE and generate an HTML-format export file, which is an old format all browsers can understand. But if Windows won't run any more, that option isn't available.

In a brief search of Apple's forums, it doesn't appear that Safari can import/convert the .url files directly.

It seems some kind of little script or utility might be needed.

In the meantime, as you use them (I think double-clicking should launch the address in your default browser) you can bookmark them directly into Firefox's bookmarks until someone finds a bulk solution.