PureBrowser displays Riot without a text box at the bottom, does not allow for scrolling or clicks. PureBrowser & PureOS updated today.
Please mention the version of PureBrowser that you do not experience the issue.
...and if that version is 52.5.0esr-1pureos2 then please test if the newer version 52.6.0esr-2pureos1 works properly too:
Either edit /etc/apt/sources.list to add the "landing" suite (in addition to "green"), update APT database with "apt update" and update purebrowser with "apt install purebrowser" (and then comment out the "landing" suite if you don't want to generally track packages when they arrive there), or manually download and install the newer purebrowser .deb package from http://repo.pureos.net/pureos/pool/main/f/firefox-esr/