In SiteStudio when trying to edit any page, there supposed to view option 'Launch Rich Text Editor' for editing the page, but it is not showing in any other browsers except Internet Explorer.
According to the SiteStudio Latest Features Reference at http://www.sitestudio.psoft.net/studio_changes.html, the latest Parallels SiteStudio version is 1.8 (you have earlier version - 1.7) and it was released on May 18th 2009. It supports the latest browsers of that time, including Internet Explorer 8, but since that time SiteStudio has not been actively developed and now is considered as a legacy product, meaning that it is not supposed to support browser versions released after May 2009.
Switch to Parallels Web Presence Builder or use the IE browser.
Parallels Web Presence Builder offers migration from Parallels SiteStudio. Please refer to the following information for more details - http://hsphere.parallels.com/docs/3.5/reseller/html/index.htm?fileName=17875.htm , https://kb.odin.com/en/8168