For anything where security matters, you shouldn't use any browser from the Debian repository, except for Firefox (formerly Iceweasel) and Chromium.
The reason is, that all other browsers run a webkit engine of some sort, which under Linux is simply in a constantly terrible state when it comes to security. [1]

I guess interacting with letsencrypt.org qualifies as security-critical, because if you can't even ensure the security on your end of the line, then using their service makes no sense in the first place.
Since Chromium isn't available for arm, Firefox is your only choice on the N900. But even that should be taken with a grain of salt because I don't know what I might have silently broken by accident, when allowing Easy Debian's glibc to be compiled against Maemo's kernel 2.6.28. And even assuming I didn't break anything (I don't say I didn't!), there's still the question if Memo's kernel is still up to handling current security issues. I'm not qualified to judge that. Maybe pali or fremangordon are.

bottom line:
For me there are just too many open questions to trust Maemo's/Easy Debian's/any browser's security chain when it really matters.


[1] https://www.debian.org/releases/stab...owser-security