How to debug Firefox problems

Bug reporting overview

Details for each of these items are covered below with references at the bottom.

1. Clear out cache, cookies and session history.
2. Remove all plugin-ins, extensions, non-default themes.
3. Restart the application and see if you are still able to reproduce the issue.
4. Startup in Safe-Mode and reproduce.
5. Try Wayland and X11 Gtk+ backends.
6. Create a new profile. (See profile manager section below)
7. Download a copy of Mozilla and see if the issue persists. [1]

These steps can help isolate where the issues may reside.

Standard troubleshooting steps

Restart Firefox

Close Firefox completely: From the menu at the top of the Firefox windowbar, select File and then select the Quit menu item. Then restart your computer and start Firefox again.

Clear cookies and cache

Many problems with loading web pages can be resolved by clearing Firefox's cookies and cache:

1. Click on the Tools menu and select Clear Recent History... to bring up the Clear Recent History window
2. In the Time range to clear drop-down menu, select Everything
3. Click the arrow next to Details to display the list of items to clear, then select the following items:
   • Cache
   • Cookies
4. Click Clear Now.
5. Exit your browser
6. Clear Flash cookies
   • find ~/.macromedia/ -type f -name \*.sol -exec rm '{}' \;

For more information, see Clear Recent History. [2]

Test in Safe Mode

firefox -safe-mode

Reset preferences

( Safe mode option ) [3]

Troubleshoot extensions and themes

Sometimes add-ons for Firefox (extensions or themes) can cause problems. To confirm whether your problem is caused by an add-on, launch Firefox's Safe Mode:

1. Close down Firefox completely: At the top of the Firefox window, click the File menu, and select the Quit menu item.
2. Go to your Terminal and run: firefox -safe-mode
3. In the Firefox Safe Mode dialog, click Continue in Safe Mode.
4. Test for your problem.

If the problem does not occur in Safe Mode, an extension or theme is likely the cause. For more information about troubleshooting extensions and themes, and how to narrow down which add-on is causing problems, see Troubleshooting extensions and themes. [4]

Troubleshoot Add-ons / plugins

Sometimes plugins for Firefox (such as Adobe Reader, Flash, Java, RealPlayer/HelixPlayer, Rhythmbox, Totem and VLC) can cause problems.

1. Open the Add-ons Window by clicking the Tools menu and selecting Add-ons
2. Click on the Plugins icon at the top of the Add-ons window.
3. Click each plugin in the list and then click Disable.
4. Test for your problem.

For more information about various plugins, and what to do if you find the plugin that causes problems, see the Troubleshooting plugins article.

Check Wayland and X11 Gtk+ backends

Firefox can run with two independent Gtk+ backends / graphics servers. X11 is a default on all Fedoras up to 30 and Fedora 31 uses Wayland as default. Please try if your issue can be reproduced on both X11 and Wayland environments.

On Fedora 30 and older

1. install firefox-wayland package
2. close all active firefox instances
3. run Firefox on Wayland from menu or firefox-wayland in Terminal

On Fedora 31 and further

1. install firefox-x11 package
2. close all active firefox instances
3. run Firefox on X11 from menu or firefox-x11 in Terminal

Create a new profile

If the steps above don't fix your problem, continue by following these instructions.

Make a new profile

A corrupt profile can cause various problems with Firefox. You can try to make a new profile test whether that solves the problem, and if so, copy your data (bookmarks, saved passwords, etc.) to the new profile.

Important: Before you can start the Profile Manager, Firefox must be completely closed.

1. Exit Firefox. To close Firefox, at the top of the Firefox window, select the File menu, and then select Quit.
2. In Terminal run: firefox -ProfileManager
   • If the Profile Manager window does not open, Firefox may have been running in the background, even though it was not visible. Close all instances of Firefox or restart the computer and then try again.
   • If you are connected to another host, and the above is not working properly, run: firefox -ProfileManager -no-remote
3. To start the Create Profile Wizard, click Create Profile... in the Profile Manager.
4. Click Next and enter the name of the profile. Use a profile name that is descriptive, such as your personal name. This name is not exposed on the Internet.
5. You can also choose where to store the profile, which is useful if you plan on exporting your data and settings to another computer or setup in the future. To choose its storage location on your system, click Choose Folder....
6. To create the new profile, click Finish.
7. Click on the newly created profile in the Profile Manager and click Start Firefox.

Test to see if your problem occurs with the new profile. If it doesn't, you can copy your data to the new profile - see Recovering important data from an old profile for instructions. For troubleshooting purposes, only copy the files that correspond to your bookmarks and saved passwords.

Collect information for a bug report

In the URL bar, visit this link:

about:support

Copy this information to your bug report. [5]

Testing Mozilla binaries

Some issues can be Fedora specific, caused by build environment, patches and so on. It's important to try vanilla binaries from Mozilla project to negate that case.

1. Download Firefox [6]/Thunderbird[7] from Mozilla site directly .
2. Unpack the tarball.
3. In Terminal run locally as ./firefox -ProfileManager -no-remote (./thunderbird -ProfileManager -no-remote), create a new profile and test your issue.

Additional Reading

• Additional accessibility prefs can be found here: [8]

• Additional hidden prefs can be found here: [9]

• Mozilla's own basic trouble-shooting page: [10]

• Mozilla support page: [11]

• Bug info Firefox: Bug_info_Firefox

• StackTraces - Firefox: StackTraces#Firefox