hi, download the full installer for the current firefox version for your system & language from https://www.mozilla.org/firefox/all/ then reboot your pc once and run the setup file you've just downloaded. hopefully firefox will open up again afterwards.

Note that an error message about XPCOM missing or about platform version usually happens because of a failed Firefox update that left you with a mixture of old and updated files in the Firefox program folder. This can happen in case security software was keeping a handle of some of the files in the Firefox program folder preventing Firefox from replacing all the files. You can do a clean reinstall to ensure that all files are replaced. You may have to disable security software temporarily in case the problem persists.