PureBrowser currently (since 60.1.0esr-2pureos1 released to landing on August 17th) lack a start page.
Removal of hidden system add-on Activity Stream leaves PureBrowser with a blank start page in since Firefox 57: Use of chrome page about:home has been removed upstream.
One option is to patch code to revive use of chrome page (still in source, but possibly not for long).
Another option is to provide a plain html file, and patch runtime configuration to use that.