Like any program, there are times when the Firefox browser occasionally slows down or hangs. Firefox slowdown can occur for a number of reasons, primarily related to outdated Firefox versions or slow extensions. In some cases, Firefox itself isn't to blame -- other programs or website scripts are. Before you can fix a slowdown, diagnose the cause with a few important troubleshooting steps.
Sometimes Firefox simply needs to be updated. Out-of-date versions may not interact well with your current extensions, or may have performance issues fixed in later releases. Usually Firefox will automatically prompt you to update, but if you aren't receiving these prompts, you can manually update Firefox. Click the menu button, shaped like a stack of horizontal bars, then click the Help menu button, resembling a question mark in a bubble. The "About Firefox" option opens a small window displaying the current version, along with a button to update if Firefox is out-of-date.
Disable Extensions and Plug-Ins
Extensions and plug-ins are also a common cause of slowdown in Firefox. Exactly why depends on the extension or plug-in itself: Some drain system resources like RAM and CPU processing power, while others require time to load and update their elements properly. Sometimes individual add-ons are fine, but create slowdown when forced to share resources with other add-ons. Finding which add-ons are causing Firefox to slow down is a systematic process, requiring you to disable add-ons one by one and gauge any performance changes. Extensions and plug-ins are managed from the "Add-Ons" menu.
Disable Unnecessary Scripts
Website scripts can also create slowdown, especially on sites that make extensive use of scripts. Unresponsive or broken scripts create prompts, asking if you want to close them or let them run. Closing them should quickly fix the problem, although in some cases the script just needs more time to finish loading and will run fine once finished. NoScript is an add-on Mozilla recommends to combat this problem, by enabling you to select what scripts run on which websites.
Close Unneeded Programs
In some cases, other programs are the actual cause of a Firefox slowdown. Firefox draws from the same pool of system resources as other programs, so when resource-intensive programs run alongside Firefox, overall performance may suffer. Close out any programs you don't need running -- in most cases, you should see an immediate upgrade in performance.
If nothing else seems to work, reset Firefox to its default settings. This option uninstalls all add-ons and deletes all non-essential information, so back up your bookmarks before starting. To reset Firefox, click the menu button, followed by the Help menu button and "Troubleshooting Information." The "Reset Firefox" button in this menu begins the reset process.