When I first made this extension, there was no way to hide all the activity details on cards. The list was full of entries like "So-and-so moved this from X list to Y list" and "So-and-so completed X item on this card". Useful comments left by users got lost.
Since that first release, Trello added a "Hide Details" button which hides activity by default on all cards. Which is great! The only trouble is that this choice is not remembered if you log out or clear the cookies on your browser. This extension activates the Hide Activity button, if's displayed, when you open a card.
The previous version of this extension hid all the unnecessary activity well enought, but unfortunately made it impossible to view activity again without disabling the extension. And due to the way Trello works, older comments might not have been loaded.
Version 2 hides activity in a much smarter way. Instead of blocking them on the page, it triggers Trello's own "Hide Details" button — which means that all comments are loaded by default and you can view activity again if you want to with the "Show Details" button. When you open the card later, activity will be hidden again.
Please note: 1) this extension does not stop Trello tracking activity, 2) it only hides activity on the card view. Activity is still available on the Board menu and there are no plans to change this.
This extension is only tested in the the most recent version of Chrome. If reporting a problem, please try to be as specific as possible (e.g. what is not working and where, in which circumstances, etc).