Show Parent Folder is the ANSWER! Rated 5 out of 5 stars

If you need to be able to search not only bookmark names but also data within the description, tags, or other data fields
in a bookmark,SHOW PARENT FOLDER does it perfectly!

After installation, just open bookmarks page (not just the sidebar) and right click on the column bar to add those columns (ie: Description, Tags, etc) you wish to be included in your searches. If you don't select a particular column, the data contained in it will NOT be searched.

Once the columns are selected, the contained data will be included in searches from either the main bookmark window or the sidebar.

I can't believe Mozilla does not make global searches of bookmark data possible but at least this add-on does.

The other add-on, Go Parent Folder is absolutely excellent! It allows you to find the parent folder for any line item in your
search simply by right-clicking on the item and selecting "Go Parent Folder". If you have hundreds of bookmark folders,
you will absolutely appreciate this little add-on!