I've done the "how to speed up FF"" stuff for the last couple years.
It's fairly simple to do when you find a good article or post step by step, but there is a risk & a warning before going forward to do it.

I always back up my profile and always have a second browser to use just in case it messes up and I have to re install it.

I do set all my browsers to clean out cache & cookies when I close it, except for the special ones that I add to the exceptions section.