As Shashi has requested, please provide screen shot of issue, Pega version, browser version.
Also clarify, if it is a question of just display or functionality. Does the button click work even though it is partially visible? Does the button show and work correctly on another browser say, Chrome or IE?
Can you tryi logging in as Administrator@pega.com, and run one of the Out of the Box flow PegaSample-CustomerRequest.NewWork (O)R PegaSample-Task.BaiscProcess in Firefox and let us know if the issue shows up there as well ?
Also, UI gallery samples, dont they also not show up correctly ?