There is no such thing as security.
Security is relative.
Of late, for a long while now, including currently, SeaMonkey has been, is, late in getting security fixes.
Times past, there was actual community within Mozilla, with everyone connected to Mozilla.
Times past, there were actually more then (the current few) people working on SeaMonkey.
Times past, SeaMonkey releases including security fixes would be on par with FF.
That ship has sailed.
Mozilla answers to no one except for the almighty $$.
Mozilla has gutted everything - except that which it cares about (& that is hard to understand just what that is, because all they care about is $$).
SeaMonkey & any other project, including technologies, out their that is not... "Quantum" is up the creek. (At least some ships are still sailing.)
And then there is that little old thing called, Chrome.
Which now owns the browser & essentially the Internet.
(Now why does Mozilla exist?)
Anyhow, LONG LIVE SEAMONKEY
.
I'll use it, until I can't.
WG9s has builds, 2.49.5, that may be slightly more current, security wise, or 2.53, that are more current (though probably not yet current enough).
(He also now has 32-bit Windows builds, which he hadn't before.)
https://www.wg9s.com/
Both his 2.49's & 2.53's should be good (stable) to use.
(Always backup first, in any case.)
Security is relative.
Common sense goes a long way.
Preventive measures go a long way (think NoScript, & uBlock Origin).
I would be more concerned about the site that I have given my information to giving that away (through outright stupidity [what are the chances] or getting hacked [what are the chances]) then my browser being exploited.
Security is relative.
Take a look at addons.mozilla.org.
IMO, that place is a landmine.
Read & weep,
Blocked.
It's like with wild west - anything goes. Literally.
What good is a "secure" browser, when its (web)extension system is totally inept.
it doesn't make all the fixes to known issues that affect SeaMonkey
How does this person know what issues affect SeaMonkey?
As issues become aware, I'd think they'd be assessed & if they do affect SeaMonkey, they'd be backported (from FF).
That is (at least) the intention. (There are only so many, & they can only do so much...)
Though I've faith, it will be done, sufficiently, to keep us sufficiently safe.
Fire 750, bring back 250.
Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.1.19) Gecko/20110420 SeaMonkey/2.0.14 Pinball CopyURL+ FetchTextURL FlashGot NoScript