first of all, thank you for the purchase and for the kind words!
I will address the issues in the same order:
1). I’ve checked the background image in the theme in Firefox 33 to 37 (which is the latest version) on both OS X and Windows computers, yet I don’t seem to be able to replicate the bug. Could you please tell me which Firefox version you are using (you can find out by clicking the question mark icon and then “About Firefox” in the browser menu), and which operating system you’re working with? Also, please try removing the existing image from the Theme Options panel, clicking on “Save All Changes”, and then uploading another image. Finally, in case the website under discussion is available online, it would greatly increase the precision of my recommendations if you could provide the URL of the live version so I can see the actual code; if you don’t wish to disclose it here, you can send me an email to firstname.lastname@example.org.
2). Could you please provide a screenshot of how it looks on your mobile phone, mentioning which parts/elements of the website do not render well? Thank you, and sorry for so many requests – it’s just that in order to be able to resolve code-related issues, lots of input data is usually needed to rule out various scenarios.