Your no suppose to do what you did. There are Firefox FAQ on how to do this correctly-you need to look those up and read how to do it correctly.

''<p>KLund1100 [[#question-1493423|said]]</p>'' <blockquote>On the new computer I installed FF. opened it, closed it, copied the file/directory to the new system. '''There were already to profile subdirectories present. I just added mine.''' Now FF crashes. </blockquote> Normally, there would be two profile folders in %APPDATA%\Roaming\Mozilla\Firefox\Profiles * [random11].default * [random22].default-release If you put a new folder here, Firefox won't actually see it because it relies on a pair of .ini files to know what profile folders are in Profiles. So dropping a new folder here should not cause any issues. HOWEVER, if the pasting process merged files into an existing profile, it probably got corrupted and you would need to start again. What I mean is, start Firefox in the external profile manager by adding a space and then -P to the path for firefox.exe (you can paste this into the Windows search box or Windows run box): "C:\Program Files\Mozilla Firefox\firefox.exe" -P Create a new profile in that window with a unique name like FEB2025 to get a clean start and test whether Firefox can run in the new profile. Success? Okay, after that, you can try transplanting a folder again. (This is an example, but needs to be adapted to using your backup as the source: https://support.mozilla.org/en-US/questions/1474421#answer-1687884) By the way, do you use the same Windows username on both systems?