Modern browsers can save changes in local storage. This feature is automatically engaged when editing from a server you don't own (or aren't logged in.)
Here we list changes you have made and have stored in your browser. You can review changed pages and discard those you no longer want.
Notice: this is an under developed experimental feature. It takes some ingenuity to even see what it is doing. However, you will know you are seeing a locally stored page when it has a yellow border.
If you make local changes to another site, you may be able to offer those changes to the site owner using the Submit Changes mechanism.
If you make local changes to a site you own, you can selectively publish local changes to that site by logging in and then forking [⚑] each local page you want to save.