Why don't you simply update your web browser as I advised you to do in another post you posted in here?
Nervous about upgrade to El Capitan
That is your easiest way to stay secure on the OS X version you are running.
Firefox ESR here.
https://www.mozilla.org/en-US/firefox/organizations/faq/
There is a lot of work to upgrading/updating to a new OS X version.
See my link below in my reply to the Original Poster (OP).
Updating your web browser to be more secure is the quickiest and easiest solution to solve your security problem on OS X 10.7 Lion.
Especially if you can't upgrade your Mac past OS X 10.7.5 Lion.
Here are the Mac hardware requirements for macOS Sierra.
MacBook (Late 2009 or newer)
MacBook Pro (Mid 2010 or newer)
MacBook Air (Late 2010 or newer)
Mac mini (Mid 2010 or newer)
iMac (Late 2009 or newer)
Mac Pro (Mid 2010 or newer)
These Macs need to be running OS X10.7.5 or later OS.