"ForecastFox" is incompatibility with Nightly This add-on is not compatible with your version of Firefox because of the following: Mozilla has marked this version as incompatible with your Firefox version. Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:34.0) Gecko/20100101 Firefox/34.0 ID:20140825030205 CSet: daa84204a11a
This is not an e10s bug. ForecastFox simply does not support recent versions of Firefox. The add-on has not been updated since 2012.