Try a new profile.

• Profile Manager - Create, remove or switch Firefox profiles

Why doesn´t starting in safe mode solved the problem?

Thank you for answering my question. I've tried a new profile and it does solve the problem as long as I keep it "clean". As soon as I restore the new profile with a backup from the previous profile, I restore the problem too. Meanwhile I found out that if I "drag and drop" a file to a new mail I can attach it. But the problem remains in other sites that don't have the "drag and drop" option. I've imagined that the problem might be with some of my addons, which I'd like to keep the most of them, so I've tried to figure out which was causing the problem using FECT. The problem always persisted and I wasn't able to do so. Which led me here, hoping that you can help me, like you did before, and answer to some of my new questions:

1. Is there any other way to figure out what's causing the problem (besides "trial and error")? 2. Is it possible that the problem isn't caused by any of the addons? 3. If the problem is not caused by any of the addons, what can be causing it? 4. If the problem's solved in a new profile, shouldn't it be solved in safe mode too?

I thank you very much in advance for your attention, hoping that you can help me avoid having to create a new Firefox back from the start.

To answer your first question, though you have answered it by inference :-), Safe Mode disables add ons and preferences that may have been changed in other modifications.

It also does not disable extensions, disabling them one by one might give you a better idea to narrow down the cause as well.