OK, Sorry about that. Follow these instructions. Note they look similar to the tabSearch, but the name of the preference is different.

Type about:config in your browser's url bar.

Click "I'll be careful, I promise"

Right click and select New->Boolean

For the preference name, type:

extensions.brandthunder.keywordSearch

set it to false.

Next, search in the filter for keywordURL

Right click on it and select reset.

Once you have done this, the keyword search should not reset itself anymore.