hi Mmikey9668, assuming that this is a question about desktop firefox... this is a problem that is usually caused by a windows system restore. please first try a clean reinstall of firefox: *download the full firefox setup file from https://www.mozilla.org/firefox/all/ *uninstall firefox on the machine *manually delete all remaining files in the firefox program folder, which usually resides in ''C:\Program Files (x86)\Mozilla Firefox\'' *reinstall firefox in case this did not help, the xpcom error message at startup might also be caused by third-party security tools: http://kb.mozillazine.org/Browser_will_not_start_up#.22Couldn.27t_load_XPCOM.22_error