Windows 7 - Firefox 3.5.6 Problems

Hi,
seem to have messed up my Firefox browser since updating to V3.5.6 yesterday.None of my add ons will work.I've been searching for solutions and one that kept coming up was to navigate to %APPDATA%\Mozilla\Firefox\Profiles and delete or modify the following files ;
extensions.cache
extensions.rdf
extensions.ini
compatability.ini
problem is that I think this was for an earlier version of windows,as extensions.ini is not there(I've enabled hidden folders).I've tried uninstalling and reinstalling Firefox with older versions and even the beta 3.6 but still the add ons won't install(error 203).It tells me to consult the error console,but I don't understand any of the entries there.
No matter how hard I try to delete all the files for Firefox,there always a couple there that it says I need permission to delete-how do I get permission if I'm the administrator?
Would appreciate any help.
Thanks.

Started in safe mode - deleting anything to do with Mozilla Firefox.Installed older version in safe mode - restarted -back to normal.Phew!

Good job, and thanks for posting the answer here. Now if others have the same problem, they can check this tread. GJ
Happy Xmas!

Must have been an isolated case. I upgraded both my laptop and desktop using Firefox's own updater and all is well.

may be of interest for you

Unable to install themes or extensions - MozillaZine Knowledge Base

Running Firefox V3.5.6 on a few notebooks with Windows 7 and usual add-on with no problems to report.

As a postscript to this problem - After sorting everything out,I foolishly tried to upgrade and messed everything up again! Spent ages deleting everything to do with Mozilla(don't forget the profile files).Booted up in safe mode but with network connection enabled, and downloaded Firefox again.When installed,but still in safe mode,I reinstalled all the add-ons sucessfully,and then upgraded to V3.5.6 .Suspecting it might be a problem with my firewall(PC Tools)or my A/V(PC Tools Spyware Doctor with A/V).Noticed that when I was having problems with the add-ons,it also affected my bookmarks(couldn't edit or delete them).Hope this might help someone else.