I just completed an uninstall of Firefox 1.0 and an install of 1.0.1, keeping all my plugins and search plugins by doing this:
First, I downloaded FFDeploy.exe from
Bob Templeton's site.
Next, I ran FFDeploy, selected the Firefox directory, did not import favorites, and did not create .exe file. Then, in the Firefox_Deployment directory created on the desktop, I deleted all but the GlobalProfiles, Plugins, and Searchplugins folders and the CreateProfile.vbs file. (CreateProfile.vbs is placed in the directory by FFDeploy.)
(Why not just use FFDeploy to make the entire installation? Because Firefox isn't technically "installed" then, it doesn't appear in the Add/Remove Programs dialog, and this allows you to use your same settings with a compatible version of Firefox, not just reinstall your original installation.)
After that, I made a WinRAR SFX file of the remaining file and folders, using the following comment:
CODE
;The comment below contains SFX script commands
Path=C:\Program Files\Mozilla Firefox\
SavePath
Setup="C:\Program Files\Mozilla Firefox\CreateProfile.vbs"
Silent=2
Overwrite=1
Title=Firefox Unattended Customization Setup
Then, I uninstalled Firefox 1.0, and manually deleted the following folder: C:\Documents and Settings\(username)\Application Data\Mozilla.
I then renamed the 1.0.1 installation "Firefox.exe", for simplicity, and ran the following using RunOnceEx:
CODE
REG ADD %KEY%\260 /VE /D "Mozilla Firefox 1.0.1" /f
REG ADD %KEY%\260 /V 1 /D "D:\Install\Firefox\Firefox.exe -ms" /f
REG ADD %KEY%\260 /V 2 /D "D:\Install\Firefox\Custom.exe" /f
(No, that doesn't mean I have 259 other programs installing before Firefox...

)
All settings are intact. It's like I never uninstalled it at all. Windows even still recognized Firefox as the default browser.
I don't have a very complex installation of Firefox, so this works for me...just thought I'd share my way of doing it, in case somebody happens to find it useful.
EDIT: I've never tried doing it this way with extensions, but there is an extensions folder in the Firefox_Deployment folder after FFDeploy runs - if somebody is willing to try it, let us know how it works.
Also, when Firefox runs for the first time on a new machine, it will ask you if you want to set it as the default browser. To prevent IE 6.0 from nagging you about being the default browser, put the following registry key into your registry tweaks:
CODE
[HKEY_CURRENT_USER\SOFTWARE\Microsoft\Internet Explorer\Main]
"Check_Associations"="no"
I haven't verified this is the only registry tweak needed to prevent IE from nagging you - there may be, and are probably, other tweaks which do the same thing, and I will update as I find them.
Overall - this allows for somebody with intermediate skills, who isn't a programmer, to easily create a custom Firefox installation.