→ → Firefox Compatibility Mode
Enable Firefox Compatibility Mode to install add-ons from Mozilla add-ons website
Open PureBrowser and type about:config into location bar and hit Enter, a warning will popup:
Click I'l be careful, I promise! button, and type useragent.compat into the search bar, then double-click the preference to change its value to true:
You will also have to change your useragent string to install Firefox addons.
To do this, open about:config, right-click, select New -> String , enter general.useragent.override, and enter Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Firefox/60.0 as a string value. Then, click "Okay" and reload the page.