One of the main causes of problems with Firefox is out of date plugins. To help counter this Mozilla have developed a plugin checked which will inform you if your plugins are up to date and give links to update old plugins. There is nothing to install to use the plugin checker, just visit this site – https://www.mozilla.com/en-US/plugincheck/
It can detect many of the popular plugins.
This site is specifically designed for Firefox and may not work in other browsers. It may work in Gecko based browsers such as SeaMonkey and Flock, but I do not have any installed to test it.