How can I apply cpu and memory limit to "Web Content"?

I tried to put memory limit on programs, by using their desktop shortcuts in order to apply the same limit for their child process too. I found that "Web Content" is a separate process in what is web content and it uses high memory not only in my computer. I am using for instance for Firefox and child processes in Firefox's .desktop shortcut having an execution line:

Exec=sh -c "ulimit -m 131072;nice -u username 19; cpulimit -l 25 -- ../firefox/firefox/firefox"

Although sometimes, Firefox uses a little bit higher than 25(i.e 26,27) but it seemed that it worked. Also GeckoMain is limited in terms of cpu. However, I noticed that process named "Web Content" continues to use much higher CPU when Firefox is open. How can I apply cpu and memory limit to "Web Content"?