How to synchronise bookmarks between Google Chrome and Opera?

Transmute will convert, synchronize, sort, organize and remove duplicates from your bookmarks and more.

Transmute supports all of the major web browsers including Google Chrome, Mozilla Firefox, Internet Explorer, Opera, Apple Safari, Chromium, Flock and Konqueror!

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note: automated/scheduled cross-browser conversion is only available in the Pro version ($20).

Xmarks is what you're after. There is also BookmarkSync which sits in your system tray.

http://www.xmarks.com/ -- web site says it works on Opera, I've used it on Firefox and Chrome, works very well.

One more way to use Google Bookmarks in both Opera and Chrome (and probably any other browser):

1. Add a bookmark to Google Bookmarks
   1.1 Chrome and Opera both have extensions to add pages to Google Bookmarks
   1.2 Or use the 'Google Bookmark' bookmarklet found at the bottom of the Google Bookmarks list
2. Add a custom search engine to search for your bookmarks using the address bar. For example gb bookmarks will search for bookmarks tagged or named 'bookmark', where gb is the keyword for the Google Bookmarks search engine.

The idea and instructions on how to create a Google Bookmarks search engine come from here: https://metaed.blogspot.com/2008/12/using-google-bookmarks-in-google-chrome.html

The article describes how to create this search engine for Chrome, but the same instructions work for Opera.