Can you please elaborate on what you are trying to do? Also, please note that the version of Firefox you are running is VERY out of date (48, the current version is 62). This is because you are running a VERY old version of Mac OS (10.7). Apple offers free updates to modern versions of Mac OS for many computers. You should be able to update to Mac El Capitan, https://support.apple.com/en-us/HT206886 at least for free. You may also be able to update to Mac High Sierra https://support.apple.com/macos/high-sierra however you should update to El Capitan first. AFTER installing the Mac updates (which will bring better performance, stability and security to your computer) you can update Firefox.