The issues revolved around SiteAdvisor's installation & its updates, not Firefox's! My Firefox updated today too. Think it wants us to download FF 2! I think one new browser at a time is enough for now (just let IE 7 through).
Addendum --from MozillaZine:
Firefox may fail to open after installing or updating the McAfee SiteAdvisor Firefox extension [3] or after an update to McAfee software that includes the SiteAdvisor component [4]. According to this SiteAdvisor support article, the problem occurs because of a conflict between SiteAdvisor and automatic proxy configuration scripts in Firefox. Either end the firefox process that remains in memory, start Firefox in Safe Mode and uninstall the SiteAdvisor extension from the Tools -> Extensions window or follow the workaround given in the SiteAdvisor support article. If SiteAdvisor is installed as part of a McAfee software package such as McAfee Internet Security Suite, you can selectively remove just the SiteAdvisor component using the McAfee uninstaller, e.g., via Windows Add/Remove programs. [5].
Addendum --From McAfee:
Solution
There is currently a conflict between SiteAdvisor and automatic proxy configuration scripts in Firefox. To get SiteAdvisor installed you need to temporarily disable your automatic proxy configuration script.
If you have already used Firefox's safe mode to remove SiteAdvisor and want to reinstall it:
1. Install SiteAdvisor from:
http://www.siteadvisor.com/download/ff_preinstall.html2. Exit Firefox
3. Start Firefox in safe mode (Start, All Programs, Mozilla Firefox, Mozilla Firefox (Safe Mode)) and change the connection setting (Tools, Options, General tab, "Connection Settings") to "Direct connection to the Internet"
4. Exit and restart Firefox; you should be prompted to accept SiteAdvisor's license agreement
5. Return your connection setting to your automatic proxy configuration, then restart Firefox
If you are stuck and cannot start Firefox and want to get SiteAdvisor installed:
1. Press Ctrl+Alt+Del, (click Task Manager if it does not display), click the Processes tab in Task Manager, if "firefox.exe" is listed in the Processes list, click to select it then click the "End Process" button
2. Close Task Manager
3. Start Firefox in safe mode (Start, All Programs, Mozilla Firefox, Mozilla Firefox (Safe Mode)) and change the connection setting (Tools, Options, General tab, "Connection Settings") to "Direct connection to the Internet"
4. Exit and restart Firefox; you should be prompted to accept SiteAdvisor's license agreement
5. Return your connection setting to your automatic proxy configuration, then restart Firefox