Bug 1790646 Part 1 - Preland new PIP explainer message string. r=flue…

…nt-reviewers,flod DONTBUILD

It's later in the cycle than we would want to enable this string, but there's
no reason not to go ahead and land it. We'll switch it on later.

The purpose of this change is to make the string shorter, primarily in locales
where "browse" or "Picture-in-picture" translates to something significantly
longer. This should reduce the height of the full explainer box for those
locales, hopefully decreasing the chance of it running into the video controls
or some other page element.

Differential Revision: https://phabricator.services.mozilla.com/D157265

toolkit/locales/en-US/toolkit/global/videocontrols.ftl

@@ -42,6 +42,7 @@ videocontrols-picture-in-picture-toggle-label2 = Pop out this video
 # button. When using this variation, this string appears below the toggle when the
 # mouse hovers the toggle.
 videocontrols-picture-in-picture-explainer2 = More screens are more fun. Play this video in Picture-in-Picture while you browse.
+videocontrols-picture-in-picture-explainer3 = More screens are more fun. Play this video while you do other things.
 
 videocontrols-error-aborted = Video loading stopped.
 videocontrols-error-network = Video playback aborted due to a network error.