Should firefox be running js and xml files? And should it have a chrome folder?

The google chrome thing might just be coincidence.

When my firefox gets slow loading a page it shows a message like “A script is causing firefox to run slowly… blabla.js” and less often with an .xml file. These files always seem to be local and I know some js files are junk squared so I’m a little worried. I could try reinstalling firefox but this entire computer is basically on it’s deathbed.