Has anyone else had trouble getting the mozilla "family" of apps (mozilla, firefox, thunderbird) to display on fvwm?

I'm running gentoo on amd64.

All three applications listed above will run and display on other desktop systems and window managers, as well as to remote X sessions.

However, when I run any of those three in an fvwm session on the local machine (either on the local desktop or through a vnc session), they don't display, unless I first:

1) Make the fvwm pager display 5 desktops.
2) Select desktop #4 (the last one, since they are zero-indexed) and then come back to desktop #0.

After that, they run fine.

When I say "won't display," I mean that they seem to run fine (which is to say, they're running as processes), but they don't show up on the screen.

Has anyone seen anything like that before?

I've searched my .fvwm2rc file for any special treatments of "mozilla," and there aren't any. I'm not sure what to look at next.

I was running fvwm for 2 years and never had any problems with any X related applications like mozilla. Do you have applications starting on specify desktops?

Used both fvwm and Firefox/mozilla for many times.

What version of fvwm are you using, have you upgraded it anytime recently?

The fvwm version is 2.5.12 (the latest for my system on gentoo).

I used to use mozilla on fvwm (back in the day) with no hitches.

I've looked through my .fvwm2rc file to see if there was anything specifying particular desktops for any mozilla-related applications, and there isn't. I can't find a system.fvwm2rc file (none in /usr/share/fvwm or in /etc).

epiphany works, which uses the Gecko display engine.

For now, I have to assume it's some kind of configuration bit somewhere. I'm just not sure where else to look.