What OS are you running, Linux or Android ?

Reinstall with Current Release Firefox 61.0.2 with a Full Version Installer

• https://www.mozilla.org/firefox/all/

If that does not fix the issue the issue is in your Profile : Make a new one and test ...:

• https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles

If is your Profile :

• https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile
• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

Do the above with Firefox closed. Work with Copies only, do not transfer the problem into the new Profile.

What's What in the Profile :

• bookmarks and history: places.sqlite
• bookmark backups: compressed .jsonlz4 JSON backups in the bookmarkbackups folder
• cookies.sqlite for the Cookies
• formhistory.sqlite for saved autocomplete Form Data
• logins.json (passwords) and key4.db (58+) or key3.db (57 and older) (decryption key) for Passwords saved in the Password Manager
• if you only have key3.db then make sure to remove an existing key4.db
• cert9.db (58+) or cert8.db (57 and older) for (intermediate) certificates stored in the Certificate Manager
• if you only have cert8.db then make sure to remove an existing cert9.db
• persdict.dat for words you added to the spelling checker dictionary
• permissions.sqlite for Permissions and possibly content-prefs.sqlite for other website specific data (Site Preferences)
• sessionstore.jsonlz4 for open tabs and pinned tabs (see also the sessionstore-backups folder)

Please let us know if this solved your issue or if need further assistance.

My OS is Windows 10 64bit

I have deleted all files of firefox even profile

And I've been installing version 62.0.2 64bit

I've created new profile and still same problem

I don't know what should I do please help me

This issue would normally be fixed with a clean reinstall that involved deleting the Firefox program folder.

• (64-bit Firefox) "C:\Program Files\Mozilla Firefox\"
• (32-bit Firefox) "C:\Program Files (x86)\Mozilla 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. 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.

You can find the full version of the current Firefox release (61.0.1) in all languages and all operating systems here:

• https://www.mozilla.org/en-US/firefox/all/
• https://www.mozilla.org/en-US/firefox/61.0.1/releasenotes/

I was able to solve the 'xpcom missing error' I got for a long time as Thunderbird wouldn't start when my computer started.

Open the 'Task Manager' on the menu by right clicking in Windows 10 task bar, next to the empty space on the bar showing the time and date.

On the task manager menu top menu click startup, right click on Thunderbird and select "Open File Location". If the File Explorer opens on C:\Users\(Your PC Name) \AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup, delete the Thunderbird file there.

Then, open in File Explorer the C:\Program Files (x86)\Mozilla Thunderbird directory. Find the application Thunderbird (.exe) and right click on it. Click "Create Shortcut" and confirm to place the shortcut on the desktop. Cut paste the Thunderbird - shortcut file from the desktop to C:\Users\(Your PC)\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup.

This worked for me after trying all the options of deleting and install/uninstalling the software and registry etc.

If any help on above kindly email me on kamleshbarot@revivalhotel.com

An 'xpcom missing error' is always a problem with files in the Firefox program folder and is usually caused by security software that is locking files and preventing Firefox from replacing all the files.

You always have to remove the Firefox program folder and possibly disable your security software or boot Windows in Safe Mode to get a clean reinstall. Your steps may have worked if you rebooted a few times in case an update didn't complete properly.

Hi kamleshbarot, this happens to be a Firefox thread, but you can find Thunderbird threads mentioning XPCOM using this search:

https://support.mozilla.org/search/advanced?q=%22xpcom%22&product=thunderbird&sortby=1&a=1&w=2