Multiple Processes

Hello. My tablet, has limited memory, due to its age. I am now finding that one of the main reasons why it is so slow is because whenever I open firefox, it opens multiple firefox processes which drain the memory and in some cases crashes the system. I have followed all the advice given to reduce these multiple processes, however nothing seems to work and at least 6-8 firefox processes open each time I open it. I have unchecked the recommended performance settings as well as hardware acceleration boxes. However, I cannot find where to set the content process limit to 1. Please tell me how to do this and if there anything else I can try to stop it opening multiple processes or I may be forced to ditch Firefox altogether for an alternate such as Bing, Chrome or DuckDuckGo. Many thanks. Charlie