→ → 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:
In recent versions of PureBrowser this is already set to true so you don't have to change it.
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/68.0.2 as a string value. Then, click "Okay" and reload the page.