Restarting Tor Browser – which automatically happens when closing the last tab – also causes it to restart its built-in Tor daemon. This can take a significant amount of time (certainly much higher than the 50 ms responsiveness threshold web developers seem to like talking about). When I use Tor Browser, I have a habit of opening a new tab before closing the last tab, to prevent this from happening; I would rather not have to do this.
In theory, there are two ways of solving this problem:
- Make Tor Browser use the existing, system-wide Tor daemon. This has the advantage of making the first Tor Browser startup fast as well.
- Make Tor Browser’s built-in Tor daemon persistent. This has the advantage of working, even where there is no system-wide Tor daemon.
Are either of these possible?
The closest I got to an answer is the FAQ “Do I need both Tor Browser for Android and Orbot, or only one?”  (emphasis added):
Orbot on the other hand is a proxy that will enable you to send the data from your other applications (E-Mail clients, instant messaging apps, etc.) through the Tor network; a version of Orbot is also inside of the Tor Browser for Android, and is what enables it to connect to the Tor network. That version, however, does not enable you to send other apps outside of the Tor Browser for Android through it. Depending on how you want to use the Tor network, either one or both of these could be a great option.
So it sounds like the answer is “no” on Android, but what about other platforms?
I also found an answer that confirms that Tor Browser uses a separate Tor daemon, but does not say whether it is possible to change this.
 Also available without using Tor.