I ended up having two malicious addons installed in my firefox/extensions directory:
I immediatly deleted them as I never authorized anything to install, addons nor any software.
These addons contained multiple native xpcom components.
pdfforge added a toolbar.
Here is additional info about these addons:
I didn't installed PDFCreator recently, but I used it! It should have automatically install this stuff.
Kris, Tyler: can one of you please check if the installer silently installs any add-ons or does anything wrong?
This does install an addon, but it seems to be just there to convert pages to PDF's and doesn't install silently or anything.
Hm. Did you keep a copy of the add-ons? I was under the impression that @mybrowserbar.com add-ons were all pretty much the same search toolbar crapware, without any real functionality.
There doesn't seem to be any pending actions here. Please reopen if there's more information that warrants reconsidering.