I too experience this bug and am able to reproduce it 100% of the time with every Firefox version (0.9 through 1.0.4):
1) Visit CNN.com
2) Have CCleaner clear Firefox cache
3) Reload page
You'll notice the CSS stylings have been lost and page reloads won't restore them. Only closing out the browser will reset things to normal. I've also experienced entire websites no longer loading after performing a clean with CCleaner while Firefox is open.
The advise of closing the browser before cleaning, while valid, is inconvenient.
admin, you may want to look in to the X 0.6.3 cache cleaning firefox extension:
It's capable of clearing the Firefox cache while avoiding the bugs others here have mentioned.
When cleaning the cache via CCleaner the files in the following folders as well as the folders themselves are deleted:
When cleaning the cache via X 0.6.3 the folders are emptied instead of deleted. But here's where the greater difference lies... After the 'Cache' folder is emptied, the follwing four files are re-created:
The 4 files in the Cache folder are all reset to 4096 bytes. Getting rid of these four files without allowing Firefox to recreate them is what appears to be the cause of the display bug.
There's probably nothing CCleaner can do about this because the X 0.6.3 extension uses Firefox's internal cache cleaning routine, which is capable of avoiding this bug. Perhaps CCleaner can look into ways of recreating these four files after it performs a clean?
Another thing I noticed, occassionally while using the X 0.6.3 extension to clean the cache... It sometimes moves the cache files from here:
...thereby leaving the 'Cache' folder empty. In these instances, the four files I mentioned were not recreated in the 'Cache' folder.
The original cache files and their sizes were kept intact. Closing the Firefox browser clears the 'Cache.Trash' folder though and the four files above are once again recreated in the 'Cache' folder. I don't know why it does that and haven't been able to faithfully recreate this scenario, but it's definitely occuring.
It seems that Firefox always must have the four _CACHE_*_files to exist in either the 'Cache' or 'Cache.Trash' folder to prevent display bugs.