I am curious if there is any application/program/plugin that will allow bookmarks to be stored in a centralized location which can be accessed by different browsers (via plugin or addons) and hopefully by multiple desktops/systems/computers.

I would think that something like this would be possible as long as the location where the files are stored allows access by multiple systems at once (server FS possibly).

If anyone knows of an application that allows this please let me know. If there is any reason that this can't be done or major issues making this difficult, I'd like to hear what they are out of curiosity. Thanks!

Different browsers use different file formats and filenames, AFAIK. You can manually export and import bookmarks, but I know of no way to do what you want.

I use an ancient php/mysql application called online-bookmarks, running on an internal web server. It works quite well for me. Bookmarks are presented as a web page which works in any browser.