First up, a way of running Firefox on old computers that are short of memory (until I discovered this, Firefox was too crashy for me to use). fyre came up with a very useful fix for this. Since he describes it better than I can, see his Firefox memory issues post. Many thanks for that one. (Note: his site is semi-down at the moment, but still just about legible.)
Secondly, I have been tearing my hair out because I couldn't get Gmail's POP3 system to work; it kept giving me a weird error message about untrusted certificates in an SSL chain and suggesting I should add the appropriate site to a trusted list, something I don't know how to do. I assumed it was a temporary blip and trustingly waited for Google to fix it. Eventually I got fed up and went poking around, and it turns out the solution was to change the POP server details to
pop.gmail.com). This may be a localization thing, but it fixed a very annoying issue for me, at least.