Need to Install - But Add-Ons?!

[Eakamai]

I know nothing of uMatrix.
This looks to be the last that mentions "firefox" (rather then webext), https://github.com/gorhill/uMatrix/releases/tag/1.1.4.

Actually had that downloaded aleady but guess i never tried it because of 'firefox' in the filename. It installed & seems to be working OK.

[Eakamai]

I have found "Cookies Exterminator" 2.9.4 helpful.
It works with Seamonkey without conversion.

The suggestion to install "AMO Browsing for Seamonkey"
is a good one.

It looks good. Thank You!