[tor-bugs] #28513 [Applications/Tor Browser]: Change SessionStore so it doesn't violate disk avoidence goal

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#28513: Change SessionStore so it doesn't violate disk avoidence goal
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     Reporter:  sysrqb                    |      Owner:  tbb-team
         Type:  defect                    |     Status:  new
     Priority:  Medium                    |  Milestone:
    Component:  Applications/Tor Browser  |    Version:
     Severity:  Normal                    |   Keywords:
Actual Points:                            |  Parent ID:
       Points:                            |   Reviewer:
      Sponsor:                            |
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 As another data point, following on #28507, we're also violating the disk
 avoidance goal because Fennec saves information about open tabs (and
 recently closed tabs) on disk in case the app is killed (see the
 [https://gitweb.torproject.org/tor-
 browser.git/tree/mobile/android/components/SessionStore.js?h=tor-
 browser-60.3.0esr-8.5-1 SessionStore]). This allows for restoring the
 browser state when the app is next opened.

 I hesitate saying we should rip this out because if we want a usable
 browser on Android, then we'll need something like this. If the app
 doesn't save state, then when the user switches to another app Android may
 kill the browser (because it is now running in the background) and the
 user will lose their entire browser session.

 Given the available options, I think we should keep the SessionStore
 enabled and rely on the #28507 preferences for clearing saved state when
 the user explicitly closes the app.

 I think we can be a little clever with encrypting the session file on
 disk, but it'll require some experimentation.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/28513>
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