Given the number of Firefox users that block Google Analytics, I wouldn’t be convinced about a 2% figure.
It also depends who the users are... given that Firefox tends to be used by many technically-inclined users, sysadmins, etc. (at least according to what I observe around me), it might be users you might want to consider, depending on what you're offering...
You can block Google Analytics all you want. Unless you're spoofing your User-Agent, servers still know what browser you're using.
The question isn't whether the server logs are there. It's whether anyone looks at them instead of GA for browser information.
But GA, statcounter et al don’t use server logs. They use JavaScript.