hello, can you try to do a clean uninstall as it's described in Desinstalando o Firefox (you don't have to delete your configuration though)

afterwards restart your pc, download a fresh copy of firefox from getfirefox.com and install that...

I make all but the firefox don't start, only the message: "Couldn't load XPCOM"

Thank you!

hello, the same issue was mentioned here: https://support.mozilla.org/questions/943596 & in this case it was apparently present when firefox was set to autorun on startup of windows.

a general websearch also suggests that it might be related to the sandboxie software - do you use that & run firefox in a sandbox?

What OS are you using on your computer? Windows XP, Vista, Win 7, Win 8, Mac or Linux?

(the OP posted with a Google Chrome user agent on Windows 7 (NT 6.1))

Quote: But the xpcom.dll is in the firefox folder, and in the system32 folder and in the system too.

If you have an xpcom.dll file in the system folder and in the system32 folder then you need to remove the file in those locations.

Firefox files should only be in the Firefox program folder.

• (32 bit Windows) C:\Program Files\Mozilla Firefox\
• (64 bit Windows) C:\Program Files (x86)\Mozilla Firefox\

Thanks for help!

I use win 7 32 bits

Is there any simple fast way to correct this "Couldn't load XPCOM" error when I start Firefox?

Thx, David A.