According to the FAQ pureos’s browser uses Tor by default. Don’t make it so hard for your users to access your website.
My pre-load of PureOS came with both TorBrowser and PureBrowser, the latter being another unbranded Firefox which does not use Tor (but does have uBlock-Origin and HTTPS-Everywhere pre-installed).
Both TorBrowser and PureBrowser are installed, and PureBrowser is the default. PureBrowser does not use Tor.
(sorry about the double-post, my first did not appear for me, might have been a cache issue)