It sure is.
On your PC (portions excerpted from this
website ):
1. Select the Bookmarks menu in the menu bar at the top of the screen, then choose Manage Bookmarks. The bookmarks management screen will appear.
2. Select File > Export Bookmarks.
3. Name your file “bookmarks.html” and save it to your desktop or anywhere else you can find it.
4. Copy the bookmarks.html file to a flash drive or a CD and attach/insert the disc or drive into your Mac.
5. Open Firefox on the Mac, choose Bookmarks -> Organize Bookmarks -> File menu -> Import -> From File, then choose the file you exported to.