Remove duplicate bookmarks in Firefox

I just installed this and was surprised at how many dups I had. Deleted a dozen or so just to check it out but will go back to it later.
" Bookmarks are both my bread and butter and also the bane of my existence. Honestly, I began collecting them in the mid 90′s and still have the same file, although a steadily added-to version of it. In the early days I backed up the file to a CD and later an external hard drive. Then Xmarks came along to save me. Now Xmarks-like ability is built right into browsers like Chrome and Firefox.
"However there are two big problems with my growing 15 year old collection — it contains duplicates and it is rife with broken links. Today I want to look at a way to solve the former and in the future we will tackle the latter. … "

January 21, 2013

Source: Ghacks Technology Newsletter
 Remove duplicate bookmarks in Firefox