Earlier quoted context omitted.
I think they are complementary, since one is about browser site isolation, and one is about process isolation on the computer. Using temporary containers, multi-account containers, site isolation, along with a number of other privacy/security addons such as Umatrix, LocalCDN, and many others, I have not noticed any slowdown. This on an older broadwell i7 with 32GB of ram.
So far it seems to work fine for me too. Can you share you list of security/privacy addons? I've used Umatrix but never heard of LocalCDN. Was wondering what other gems you may have found.
AdNauseam
Archive Page
ClearURLs
Cookie AutoDelete
Cookie Remover
Decentraleyes
DoH Roll-Out
Don't track me Google
DuckDuckGo
Facebook Container
Firefox Multi-Account Containers
Firefox Private Network
Firefox Relay
Firefox Screenshots
First Party Isolation
Google Container
Google search link fix
Greasemonkey
HistoryBlock
HTTPS Everywhere
I don't care about cookies
Laboratory
Link Cleaner
LocalCDN
PinPatrol
Privacy Badger
Privacy Pass
Redirect AMP to HTML
Skip Redirect
Tampermonkey
Temporary Containers
Trocker
Twitter Container
uBlock Origin
Ugly Email
uMatrix
Wappalyzer
Zoom Redirector