Sometimes users try to view SQL Server Reports in Firefox or Chrome Browser, it does not display at all or displays in a half screen.
They found it strange when the same report works absolutely fine in Internet Explorer.
The Solution:
Add the code below to "%ProgramFiles%\Microsoft SQL Server\MSSQL.3\ReportingServices\ReportManager\Styles\ReportingServevices.css"
.DocMapAndReportFrame{min-height: 860px;min-width: 2000px;}
Read how to display reports properly for Reporting Services 2008R2/2012.