You can take this a step further. You can copy the existing firefox.application to ~/.local/share/applications in triplicate.

Leave the first the same, but add Hidden=true, NoDisplay=true. Then rename the other two "personal.desktop" "companyname.desktop" and change the Name values inside, and add "-P {personal/companyname}" to the Exec line.

Now your application launcher, if functioning correctly, should hide the default Firefox instance (which due to stupid Firefox behavior can do... unpredictable things), and instead you can type "personal" or "companyname" to have Firefox launch with those specific profiles.

It's really quite fantastic, as good a solution as any I could ask for.

How do you keep from getting them mixed up in the task bar when they're both running?

Presumably there’s a configuration directive to change icon?

I'm 5 days, late, but yes, I changed the Icon directive, and also I use a tiling WM and different themes per profile, so there's zero chance of mixing them up.

Is the creation of .desktop files within reach of many of the poeple intimidated by command line flags?

It's a plain text format that can be generated by a program pretty easily. It wouldn't be hard to write a hybrid ebook+SPA in JS that contains instructions that would let normal people set up their own personalized shortcuts (assuming they're even on a freedesktop.org-compatible desktop environment that supports them in the first place—which is a big leap).

You can also add [Desktop action ...] sections to your .desktop file for each profile, this will add new right-click/context menu options for easy launching of the profiles from your Linux dock.

I do that for dedicated netflix profile (with company icon) having DRM enabled, very useful.

If Firefox did extend the Profile Manager to allow for this kind of personalisation and OS integration (profiles showing up as their own, customizeable launcher icon), that'd be another win.

The windows equiv is .lnk. Or in GUI windows world create a shortcut and then modify the launching parameters using properties on the lnk file. You could also drop the string into .bat/.cmd files (but that would probably leave a cmd box running in the background). Downside to .lnk files is they are binary so you have to use an editor that understands them (like windows explorer).