Reddit Comment Collapser is a free Chrome add-on developed by Reece. This tool automatically collapses subreddit comments that are not stickied from a list of pre-defined subreddits. Users can customize the add-on to hide all non-stickied comments for specific subreddits set up in the options page.

Please note that the function of this add-on may take a short period to execute as it runs after the page loads or when the tab is focused. However, it ensures that comments are collapsed only once and do not repeatedly uncollapse.

It is worth mentioning that this add-on was designed for the 'old' Reddit layout, and may not be compatible with the new layout. The developer plans to address this in the future updates.