From MozillaZine Knowledge Base
This list of the more frequently-encountered issues or problems with Firefox is organized by subject and may include links to MozillaZine forum topics and other external sources in addition to Knowledge Base articles. It is not a complete list of Firefox issues. If you don't find an answer below, you can browse all articles in the Category:Issues (Firefox), use the Knowledge Base Search function, or look through the official list of known issues found in the Firefox release notes.
Installation and updates
Bookmarks and browsing history
Downloading opening or saving files
Problems with specific websites or web features
Privacy and security