Mozilla definitely makes things worse, probably due to memory fragmentation and running out of certain types of memory.
I run both SeaMonkey and Thunderbird as I seem to be in charge of them. In eCS, after about 3 days of uptime, I'd open a tab or window and spontaneously reboot. ArcaOS doesn't do this, instead I get freezes, usually in text mode applications such as trying to run rsync to back stuff up, sometimes the desktop and often SM doesn't finish closing. Interestingly, while on dial up and using Injoy, Mozilla apps were continuously crashing on me with problems allocating JS memory. Retiring Injoy fixed that with 4 crashes in 3 months, all when querying the system about fonts.
Mozilla is just getting too big and 32bit Windows has lots of problems with OOM (out of memory) crashes that go away just by running 32 bit Firefox on 64 bit Windows. I understand that Chrome is even worse as it spawns more processes to sandbox various things, so moving to Chromium isn't a simple solution. Our platform is an old design and the designers probably never imagined running stuff like Firefox.
As for crashes when opening the volume control, I had that at one time with the work around that I could load the DOS driver for my sound card first by opening a DOS session and then no crash. Turned out to be a faulty CPU, or at least when I swapped my Cyrix 686 that had overheated a few times due to bad fans, with a real Pentium, the crashes went away as well as all the sys3075's I had with Netscape.