These are some of the issues I ran into using Firefox preview. 1) PDF files won't download properly. A file is created but it is only about 70kb and it cannot be opened. 2) tabs reset. After sometime instead of pointing to the page or maybe reloading it, about:blank is displayed. 3) Facebook videos won't play in Facebook page instead they open in their own page. This is especially inconvenient when you consider that buy pressing back button you will go to the top of Facebook feed not where you were. 4) linked that are supposed to be open by other apps don't work. For example in google maps when you send location by email, if default browser is preview, it gives an error message. Positives: Location of address bar, privacy features, speed Excellent work and please let me know if there are anything I can do to help.