Inject automatically on install etc., add mime types, and fix nits.

go-back-with-backspace/readme.txt

 Go back with the backspace button! This extension re-enables the backspace key
 as a back navigation button -- except if you're writing text.
 
 Before Chrome 52, the backspace key navigated back (if you weren't writing
 text). Many people lost their progress while working online by accidentally
 pressing backspace and leaving a page -- so we removed the feature from Chrome,
 and created this extension for those who prefer the old behavior.
 
-After this extension is newly installed, enabled, or updated, any open tabs
-will need to be reloaded for the changes to take effect.
+This extension can't restore backspace on certain special pages, for example
+any of the "chrome://" pages such as Settings or Extensions, or in the Chrome
+Web Store.
 
-This extension can't restore backspace on certain special pages, for example
-any of the "chrome://" pages such as Settings or Extensions.
+About the requested permissions:
 
-About the "all sites" permission: In order to capture backspace on every page,
-the extension needs to install a little piece of code on each one. It does
-nothing else with the the page, its information, or your typing.
+"Read and modify all your data": In order to capture backspace on every page,
+the extension needs to install a little piece of code on each one, including
+tabs that are already open when the extension itself is installed or updated.
+It does nothing else with the page, its information, or your typing.
+
+"Manage your apps, extensions, and themes": This lets the extension detect
+when it has been re-enabled and install its code into tabs that are already
+open then, too.
 
 By installing this item, you agree to the Google Terms of Service and Privacy
 Policy at https://www.google.com/intl/en/policies/.