I recently upgraded my Firefox 2.x to 3. After that i was not able to download any files. Whenever i click on the download link, the Firefox freezes for 2-3 minutes and then ill get error message
“Unable to save to Temp folder C:\Docu~1\%User%\LocalSettings\Temp/xxxfile.part. Unknown error occured. Try saving to a different location.” The CPU usage during this time will be 99% for firefox.exe
However, i was able to download by right clicking and ‘save link as‘ option.
Things i tried with no success 
:
- Restarted Windows
- Cleared Firefox cache.
- Deleted the download history.
- Changed the default download location.
- Deleted the file downloads.sqlite in Profiles folder.
- Changed the option to ‘Always ask where to save‘ for each download.
- Cleared the various options in brower.download.xxx in about:config.
- Did a system virus/spyware scan (no virus found).
- Disabled antivirus/firewall.
- Created a new profile.
- Finally uninstalled and reinstalled Firefox.
The solution:
Decided to look more into the error message. Something was preventing Firefox from using the Temp folder. When i checked my Temp folder there were more than 55000 files and 281Mb 
. So i selected all those files (ctrl + a) and gave a shift + delete. Hmmm, it took almost 6-8 minutes for explorer to delete them.
But to my surprise my FF was perfectly normal after that.
So what was the problem? Was the Temp folder full? I d’ont know about any such limit for a folder. Who cares!
