Add another Firefox link in README.md
Add another Firefox link in README.md

andrew-sayers--frontier-forums/BabelExt,andrew-sayers--frontier-forums/frontier-forums-moderation-tools,andrew-sayers--frontier-forums/frontier-forums-moderation-tools,andrew-sayers--frontier-forums/frontier-forums-moderation-tools,Macavity/BabelExt,Macavity/BabelExt,andrew-sayers--frontier-forums/BabelExt,andrew-sayers--frontier-forums/frontier-forums-moderation-tools,andrew-sayers--frontier-forums/BabelExt,Macavity/BabelExt