Firefox load issues temporarily improved by plugging in battery

Ordinarily I use Chromium, but I’m always testing Jitsi, so today I used Firefox 68.11.0esr (64-bit) on Debian Buster. I generally start my laptop on battery. Load was getting high (often near 2.8-3 but dropping down to 1.8 occasionally; when using chromium my load in Jitsi calls feels much lower but I haven’t done systematic testing) and sound was getting a little choppy, so I plugged in the electric to start recharging the battery and instantly the sound quality improved significantly. However, after a few minutes the load again rose and audio seemed a bit uneven.

I captured output from top from during the call. This was one of the lower load readings I observed, but the only one I captured:

top - 12:11:02 up 57 min, 2 users, load average: 1.75, 1.94, 1.91
Tasks: 142 total, 2 running, 140 sleeping, 0 stopped, 0 zombie
%Cpu(s): 32.7 us, 8.1 sy, 0.0 ni, 58.1 id, 0.8 wa, 0.0 hi, 0.4 si, 0.0 st
MiB Mem : 7894.6 total, 6407.4 free, 853.3 used, 633.8 buff/cache
MiB Swap: 9536.0 total, 9536.0 free, 0.0 used. 6724.1 avail Mem

24523 cjf 20 0 9343256 567616 152744 S 123.7 7.0 53:19.64 Web Content
24465 cjf 20 0 3201692 354844 169284 S 36.0 4.4 20:39.11 firefox-esr
24676 cjf 20 0 651448 30236 24640 S 4.3 0.4 2:40.46 pulseaudio
24318 cjf 20 0 313056 55884 38788 S 1.0 0.7 0:56.30 Xorg

I have not touched the power management since I set the laptop up under Debian Wheezy some six years ago. Three major upgrades later and I believe all that is left is what is provided by the laptop-mode-tools package and whatever Debian/systemd give me by default. Oh, and I run “xbacklight -set 10” and “xset dpms 100 200 300” (but Jitsi must turn that off because my screenblanker never kicks in) when my fvwm window manager starts (yes, I’m old school).

One user in the call observed that I was listed as a speaker even though I was muted and never even tried to unmute myself. That could be another effect of Firefox, I don’t know.