One of the more frequent issues I hear from people about Firefox is that it was fantastic when they first installed it but now it’s sluggish and slow.  The problem is not Firefox, but may be your plugins and extensions.  A faulty extension could slow down Firefox quite a bit.  Here is how to identify if this is the cause of your sluggishness and spotted rendering of pages.
Step 1:  Determine if an extension of theme is the problem.
In Safe Mode, all of your extensions will be temporarily disabled and the default theme is used. This will help determine whether an add-on is causing your problem.

• Close down Firefox completely: At the top of the Firefox window, click the File menu, and select the Exit menu item.  Close down Firefox completely: On the menu bar, click the Firefox menu, and select the Quit Firefox menu item.  Close down Firefox completely: At the top of the Firefox window, click the File menu, and select the Quit menu item.
• In Windows, click Start, open the All Programs list, and navigate to the Mozilla Firefox folder. In the Mozilla Firefox folder, select Mozilla Firefox (Safe Mode).

Go to your Terminal and run:

/path/to/firefox/firefox -safe-mode

• Firefox should start up with a Firefox Safe Mode dialog.

Note: You can also start Firefox in Safe Mode by clicking Start, selecting Run (or use the Start Search box in Windows Vista) and then entering the following in the text field:

firefox -safe-mode

When the Firefox Safe Mode window appears, press the button Continue in Safe Mode.
If the problem persists in Safe Mode, your problem is not being caused by an extension or theme. It could be caused by a plugin – plugins are not disabled in Safe Mode. Check out the section below titled troubleshooting plugins.
If the problem is not present in Safe Mode:

• One of your Firefox configuration files may be corrupt. Reset your toolbars and controls to see if that solves your problem.
• The theme you’re using or one of your extensions could be the causing the problem. Continue with this article to troubleshoot.

If you have been using a new theme, switch to the default theme and restart Firefox to see if the theme was causing the problem.

• Click on the Tools menu, and select Add-ons. The Add-ons window will appear.
• In the Add-ons window, click the Themes icon.
• Select the default theme, then click the Use Theme button, to make Firefox switch to that theme.
• Close Firefox, then start it up again.

When Firefox restarts, the default theme is in use. If the problem goes away, your theme was causing the problem.

Troubleshooting plugins
If you are having problems with pages that use plugins (such as Flash, Windows Media Player, Java, and more) to display content, you may need to check to see whether a plugin is causing the problem.
Common problems caused by plugins include:

• Crashing or Hanging
• Images or multimedia items do not load
• Problems downloading

Determining If A Plugin Is The Problem

You can selectively disable plugins while Firefox is running. If you suspect a certain plugin, disable it first, then test for your problem. If you don’t know which plugin to disable:

• Open the Add-ons Window by clicking the Tools menu and selecting Add-ons.
• In the Add-ons window, select the Plugins panel.
• Select a plugin in the list and then click its Disable button. Repeat this step for each plugin in the list. You do not need to restart Firefox for the changes to take effect.
• Test for your problem. If it does not occur, go back to the Add-ons window and re-enable plugins one-by-one with the Enable button until you find which one causes your problem to occur.

If you find that disabling a plugin fixes your problem, continue following the steps in this article.

Updating or re-installing your plugins

Many problems with plugins can be solved by updating to the latest version of the plugin. You may need to uninstall and then reinstall the new version of the plugin that causes problems.
If updating to the newest version of the plugin or reinstalling it does not fix the problem, you can leave it disabled.

Manually uninstalling a plugin

If you can’t use an uninstaller program to remove a plugin, you can remove it manually:

• In the Location bar, type about:config, and press EnterReturn.
• The about:config "This might void your warranty!" warning page may appear. Click I’ll be careful, I promise!, to continue to the about:config page.
• Search for the preference: plugin.expose_full_path.
• Double-click on the plugin.expose_full_path preference in the list to change the value to true.
• Enter about:plugins into the Location bar to display the About Plugins page.
• Each entry in the About Plugins page will have "File name:" followed by a path. Use Windows Explorer to navigateNavigate to the folder shown for the plugin you want to remove.
• Rename the file to something other than its normal name – e.g. npswf32 becomes Xnpswf32

The plugin will be removed.

Re-initializing the plugins database

In some cases, you may not be able to install or re-install a plugin. Re-initializing the plugins database may fix this problem:

• From the menu at the top of the Firefox windowbar, select FileFirefox and then select the ExitQuit FirefoxQuit menu item.
• Open your Firefox profile folder.
• Delete the pluginreg.dat file.
• Open Firefox
• In the Location bar type about:plugins and press EnterReturn, to bring up the Firefox plugins list.

If you are still having issues with Firefox after you have gone through all these steps, I regret to inform you that your computer is screwed or you have a supermagnet somewhere near it.  The issue you are most likely experiencing at this point is not a Firefox issue but may be spyware, adware or OS related.  Do a full spyware scan of your computer and failing that, a reinstall of your OS.

Tags | General, Linux, Microsoft, Ubuntu