When you edit a page in the Dashboard editor you can see a preview in the editor by using the "eye" icon.
After you have saved the page you can also do a preview in the browser by clicking the "eye" icon in the menu on top.
But when you then click in the opened page on other pagelinks and want to edit them too, you have to go back to the dashboard and find the other page, by leaving the already opened page.
This is where the Frontend Page Edit plugin comes in. When you open the page as described above, it will show an additional button on the page.
By clicking this button, you will open another tab in your browser with a Dashboard that has the edit of the page already opened. Now you can start editing, withoug clicking around first. Another feature of this plugin is, that it will refresh the page in the browser where you have clicked away from, once you click on this tab again. That keeps your content always in sync with the latest changes.
You can find the Github to the plugin here: link to github