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.