Fix a couple of bugs on wordpress site

My wordpress website has a couple of bugs that I cannot fix myself. This would be an incredibly EASY AND QUICK project for somebody. The 3 things I need are: 1- Make it so that the header image does not scale when the browser is resized (happens in safari) 2- Make it so that the navigation bar is not scaled/does not move when the browser is resized (safari & firefox) 3- The navigation bar is showing a gap when looking at the website on mobile devices. I need to remove this. 4- Figure out why site appears differently in Safari and Firefox. Lowest bid that is able to do the work the quickest wins the bid. PM me for the website name as I don't want this post to show up when searching for the name. Thank you.