I thought I would followup with what I learned in case it ends up helping someone else who searches for answers to these same questions.
I originally thought that using PortableFirefox and PortableThunderbird located in my Dropbox folder would be the answer to keeping my browser and email client synced on both my desktop and notebook. I set it up, and it worked, but the syncing was not consistent enough to be a good solution for me.
For example, if I wanted to restore a previous session, with the PortableFirefox / Dropbox setup it usually failed to restore the correct tabs that had been open in my previous session - instead restoring older tabs and not showing my most recent history. It somehow kept missing my most up-to-date activity.
I also was very frustrated by a bug that is apparently very prevalent with portable apps. When pinned to the taskbar, both PortableFirefox and PortableThunderbird would each present an additional icon in the taskbar when opened. I spent a lot of time searching for a way to fix it, and finally did find what turned out to be a rather simple solution that worked. I will post that at the end of this in case anyone is interested... since most of my web searching for a solution ended up in dead ends - a lot of either "sorry, it can't be fixed" responses or really complicated patches.
I ended up removing both PortableFirefox and PortableThunderbird from my Dropbox folder. To sync Firefox, I went with the built-in sync utility that stores my information on the Mozilla servers, and it seems to be much more reliable.
For Thunderbird, I ended up just copying only the profile to my Dropbox folder and pointing the regular installations on both my desktop and notebook to that profile. That also saved me quite a bit of space in my small, free Dropbox account compared to using the portable app. You also have to change the .ini file on both devices. See the instructions here.
I basically did the same for Windows Live Mail by changing my desktop client's "store" to a folder I made in dropbox, and then doing the same on my notebook. The only issue I've had so far with that is that it seems to ask me to re-enter my password a lot, even though it was already stored correctly, and it gave me errors. (Mainly on my notebook.)
I don't think I will be able to sync my Vueminder calendar in a similar way, unless I upgrade to their portable app. The problem is that it starts up before Dropbox would have a chance to sync. I will just "backup" to a folder in dropbox, and then use "restore" on the other device to update my calendar as necessary.
I hope this helps anyone who reads this and is trying to do the same thing.
Here is how I was able to get the portable apps (PortableFirefox and PortableThunderbird) to behave correctly in the Windows 7 Taskbar:
I created a new Firefox profile by entering firefox.exe -p in the Windows 7 search box and then clicking it to run it.
(By the way, it won't work if FF is open, although you can get around that by adding -no-remote to firefox.exe -p as follows -- firefox.exe -p -no-remote -- click to run it.)
Okay...the profile wizard should be open... so give your new profile a name. I called mine FFsync
Then you need to change the default location and point it at the profile folder in your portable app:
Just browse to that folder, highlight and save it, then click Finish.
Now go to your PortableFirefox folder and start PortableFirefox.exe
Now when it's running in the taskbar, just right click the taskbar FF icon and choose "pin to taskbar".
That's it. Very simple and it works.
I did the same for my Portable Thunderbird program, and that too ran with out an extra icon in my taskbar.
thunderbird.exe -p (to create a new Thunderbird profile.)
Browse for the folder where it will be located, and choose the folder in the dropbox portable app:
dropbox\portablethunderbird\data\profile then finish.