> I hate to be That Guy, but maybe you should look into writing your own; extensions are fortunately just bundles of JavaScript.

Javascript isn't the hard part here; it's trying to figure out how to extract anything like what I need from the places.sqlite databases that hold all the relevant data.

If you trust the cloud Mozilla's client side encrypted sync service will do this.

If you want simple and dirty.

1. Create a backup of your bookmarks using the import and backup button on the Library window on each machine

2. Pick your favorite scripting language

3. merge the two json backup files using your script

Import the resulting json file in a clean Firefox profile.

> Create a backup of your bookmarks using the import and backup button on the Library window on each machine

I've tried this. The tags are not in the JSON dumps. The Mozilla people apparently believe that backing up your bookmarks means to back up everything except the tags.

A corollary: The only way to actually back up your bookmarks is to back up the places.sqlite file. Nothing else contains all the relevant data.

Tags are in the bookmark backup JSON.(Storing tags was one of the primary reasons for moving from bookmarks.html.) Search for "root": "tagsFolder" anything that is a parent of that is a tag.

Hey, thanks. Looking at a pretty-printed JSON file with that little piece of info cleared it up for me.

Wow. Okay, thanks for the information. Is there an open bug for this already? :(

Apparently, I was wrong:

https://news.ycombinator.com/item?id=4716258