Firefox doesn't have a "text fragment finding" feature built-in, so the add-on is your best bet if you are exchanging those kinds of links with Chrome users. Or you are limited to traditional bookmarks that are linked to anchor locations set by the page author, such as element id's.

Since you mentioned a post in a thread specifically, usually there is a way to extract a permalink to a post/comment/reply. That might be from a menu or from the timestamp of the post (this varies from one forum to the next).

Note that this forum has a link to a specific reply as a link that shows the created time placed under the username, other forums probably have a way to get/bookmark a link to a specific reply