Help please: Firefox seems to need "catchup time" after unlocking screen (using light-locker/lightdm)

I’ve recently switched from xscreensaver to light-locker because of xscreensaver 6.00 no longer shows the "New Login" button · Issue #125420 · NixOS/nixpkgs · GitHub

Am very happy with the switch except for the following issue: when I unlock back into my session, it appears that browsers were somehow suspended or maybe just lost network, because:

  • Electron apps show that they are reconnecting (Not really an issue)
  • Firefox appears to be doing CPU intensive work for ~2 minutes (for an overnight lock) and is unusable during that time frame. I assume it’s catching up with everything it missed?

The 2 minutes of inoperative Firefox are a real hassle.

Things that narrow it down:

  • This is on a desktop box that has continuous network access. (Not a laptop that loses wifi when lid closed etc.)
  • I’ve observed that other apps (launched from the command line prior to locking) have network access while the session is locked. (They continue serving data).
  • I’ve sshed into the box during lock and using ps/top, I’ve determined that firefox wasn’t “kill -STOPed”

So my best guess is that something tells browsers to discontinue their use of network while the session is locked. Any idea what that might be? Maybe something systemd related?

It doesn’t sound like such a terrible idea to suspend browsers while session is locked, but then is there any way to understand what Firefox is doing during these 2 minutes?