In TexStudio version 2.6.6 on OSX 10.9, pressing Fn+Left/Fn+Right in the editing area (which corresponds to Home/End on a Mac) takes one to the beginning/end of the document rather than the beginning/end of the line, which is incredibly jarring as no other program that I have encountered on a Mac works this way. This is essentially the same problem as discussed in bugs #833 and #834, but for OSX rather than Windows.
I tried using the keyboard shortcut editor to change this behavior, but the Home and End keys don't appear in the drop-down box with the list of possible keys, and if I try to set the key binding by pressing Fn+Left then instead of saving this binding it aborts and takes me to the beginning of the list of keyboard shortcuts.
Strangely, the beginning/end of document keys are shown as being bound to Home/End (based on the direction of the arrow that is displayed), but the keys they show don't appear in the drop-down box; furthermore, even when I clear these key bindings Home/End still takes me to the beginning/end of the document rather than doing nothing.
This frustrated me for months but I just found a work-around. Enter the key in preferences as (for example) fn+ctrl+right. After that in the keyboard shortcut window it will be displayed as "^\" (where the backslash is a down-right arrow). You can click between those two characters and press backspace to remove the "^" and hence the control (or command, etc) key modifier.
Alternatively, add these lines to ~/.config/texstudio/texstudio.ini:
Editor%20Key%20Mapping%20New\End=4104
Editor%20Key%20Mapping%20New\Home=4103
fixed in repository