Importing Bookmarks from Firefox (on PC) to Safari (on iPad

I have previously managed (but forgotten how) to get my Firefox Bookmarks (on my PC) into Safari (on my iPad). When I recently purchased an iPhone the "old" bookmarks on my iPad were synced to the new iphone

Since then I have significantly updated the Bookmarks on my PC and I want to get these updates on to my iPad and, consequently, on my iPhone.

Can someone tell me how this is done?