Is your browser’s download folder slowly filling up with copies of pdf’s and other files that you downloaded twice or more times?
You recognise them instantly whenever you look at the list of files in that folder
file foo.pdf file foo (1).pdf file foo (2).pdf
Here are two easy ways to get rid of these two copies:
find . -name "*\(\)*" -print0 | xargs -0 rm
ls -b *\(\)* | xargs rm