In Firefox 4.0.1 I often get "Engine already exists" popups when trying to add a new engine. I get this error for any random name that I use, which have obviously never been assigned before.
I also had this issue in Firefox 3.6. The profile from 3.6 was not carried over to 4.0, in 4.0 I used a clean profile and reinstalled all my extensions.
In Firefox 4.0.1 I often get "Engine already exists" popups when trying to add a new engine. I get this error for any random name that I use, which have obviously never been assigned before.
I also had this issue in Firefox 3.6. The profile from 3.6 was not carried over to 4.0, in 4.0 I used a clean profile and reinstalled all my extensions.