Hey there, it looks like you will need to re-install Firefox. 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. ''Kudos to cor-el for the answer to this, you can see it also here: https://support.mozilla.org/en-US/questions/1229392