Optimize profile recovery

[boolean5]

Now, when restarting a crashed browser, we archive its profile in a tar file and then extract the contents of this tar file into the profile of a freshly started browser. Maybe we could skip this intermediate step and reuse the old profile directly instead (i.e., avoid making two unnecessary copies of the profile).

Additionally, now that we will be saving the full Firefox profile (after #917), we could also look into whether we can get a performance benefit by not reinstalling the extension every time we restart a browser.