Fabio, if the extensions use JavaScript to talk to Firefox (which many many extensions do) then it would not work after an upgrade. My guess here is that during the upgrade JS went from enabled to disabled or something similar. As a side note to Alex, I grabbed the 2.0.0.5 .deb off packages.ubuntu.com and I can not reproduce with one extension. If you want me to try more, please ping me on IRC.
Fabio, if the extensions use JavaScript to talk to Firefox (which many many extensions do) then it would not work after an upgrade. My guess here is that during the upgrade JS went from enabled to disabled or something similar. As a side note to Alex, I grabbed the 2.0.0.5 .deb off packages.ubuntu.com and I can not reproduce with one extension. If you want me to try more, please ping me on IRC.