Slasher
I run both Better Privacy and Ghostery together, and no apparent problems. What
can sometimes cause an issue is if you also turn on Firefox's native "no track" option - that can allegedly slow the browser, though I've never seen it.
SeldomFixIt
For Firefox it probably easier to download it via the Firefox plugins page from within the browser.
https://addons.mozilla.org/en-US/fir...vacy-security/