Firefox was working great until a few days ago and I added some add ons. Now I can't activite Firefox and the only way I can get my emails is through internet explorer which I hate. Something is blocking Firefox and I don't know what to do

Why did you post this under Customer Service in the Business area? I've moved it here for you.

Have you tried uninstalling and reinstalling Firefox?

Fire up FF in safe mode and remove the recently installed extensions, as one, or more, are causing this issue.
Details on FF safe mode are here: Safe Mode