User Agent: Mozilla/5.0 (Windows NT 5.1; rv:13.0) Gecko/20100101 Firefox/13.0.1 Build ID: 20120614114901 Steps to reproduce: I had to repair OS (WXPproSP3). I was unable to start previously installed FF and TB, because of OS Registry rewrite. I reinstalled FF and TB in the previous locations. Actual results: I lost all FF data including Bookmarks, and all TB data including Inbox and Sent messages. Expected results: This is a request for a new function. FF and TB Installers should have detected and reported existing data files, eg Bookmarks and messages, and posed the option: Data files found - do you want to keep old data, or erase it. No file attached, no security issue. Harm (loss of data) could be done as long as this function not in TB and FF.
bug 264209 suggests that normally it will detect an existing profile. (I haven't tested)
Firefox and Thunderbird uses a profiles.ini file to determine which profiles are on a system and the installer isn't and doesn't need to be involved in any of this... it can be done entirely by the application just as reading the profiles.ini file is done by the application. Moving to a more appropriate component.