You can check for problems with preferences.

Delete a possible user.js file and numbered prefs-##.js files and rename (or delete) the prefs.js file to reset all prefs to the default value including prefs set via user.js and prefs that are no longer supported in the current Firefox release.

• http://kb.mozillazine.org/Preferences_not_saved
• http://kb.mozillazine.org/Resetting_preferences

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance).

• Do NOT click the Reset button on the Safe Mode start window.

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

Create a new profile as a test to check if your current profile is causing the problem.

See "Creating a profile":

• https://support.mozilla.org/kb/profile-manager-create-and-remove-firefox-profiles
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues

If the new profile works then you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over the problem

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

The in-content prefs are in testing right now, they aren't the default for a reason ;) Feel free to file a bug at bugzilla.mozilla.org.

I'm not having a problem to make changes to settings in about:preferences or in Options/Preferences including the connection settings, so make sure to first test this in a new unmodified profile if you can't fix this in the current profile.

• http://kb.mozillazine.org/Profile_folder_-_Firefox

cor-el, I can make changes in the Options/Preferences or in about:preferences, that is not the problem. The problem is they will not stick. Did you try this in both the current nightly and the current stable version 28?

I did not notice this issue until I changed the "browser.preferences.inContent" setting in my V28 by going to about:config and making the change to the preference setting to use the new tab based Preferences.

I then tested it in the current nightly (V31.01a1) by changing the same preferences setting BACK to the current dialog box setting used in V28.

I got the same results in each, i.e. when using the new tab based settings, any changes to proxy settings would not stick.

Did you do the exact same thing?

Current nightly version in my previous message should have been 31.0a1.

Tyler, did you try changing proxy settings as I did? If not, could you please do so. I did this:

I changed the "browser.preferences.inContent" setting in my V28 by going to about:config and making the change to the preference setting to use the new tab based Preferences. I immediately found that any proxy settings changes would not stick.

I then tested it in the current nightly (V31.01a1) which has the new tab based Preference settings enabled by default. Proxy setting changes would not stick when I used the new tab based Preferences but by changing the same preferences setting as above BACK to the current dialog box setting used in V28 any proxy setting changes did stick.

I am about to test this on two other computers in the house then in a new profile on each as suggested by cor-el. I will wait to file a bug report until I have completed these procedures, but I would be most grateful to know what results you get on your system

Thank you for your help.

Still no problems here with making changes to the connection setting in either Options/Preferences opened in the classic way or via the about:preferences page by setting browser.preferences.inContent false or true.

You can use this regular expression in the Search field on the about:config page

• /network.proxy|browser.preferences.inContent/

Did you already try this in a new profile?

Also make sure to use a separate profile for each Firefox version (release and Nightly).

UPDATE

I tested the scenario on another laptop running Windows 7 Home Premium. This laptop is not heavily used at all and has not been since it was new. Following is the procedure I followed.

I used a new Windows User account set up as an Administrator. The user account had recently been created but had not been used other than to install some basic system software and Firefox which was in version 26 at the time. The browser had not been used since.

I then completely uninstalled Firefox 26 and all user data, which was very little as the browser had only been installed and not used in this User account, using Revo Uninstaller. After doing this I rebooted the computer and logged back into the user account.

I then installed Firefox V28 as a clean install and rebooted the laptop. No add ons were added to it and I changed no settings or preferences other than the tab based Preferences as described below to test the scenario encountered on my original laptop.

Before changing the tab based Preferences setting using the standard Options dialog I changed the proxy settings with the browser still in its default install state to test if the proxy settings change stuck. That is, I changed the Network Connection settings to add a proxy address, saved the changes and exited the dialog box. I then opened up the Network Connection settings again and the changes had stuck.

I then changed them back again and checked again to make sure this change also stuck. It did.

I then typed about:preferences in the URL bar and repeated the above steps. Neither change stuck.

I then typed "about:config" without the quotes in the URL bar then "browser.preferences.inContent" in the Search field and double clicked the entry to change the Preferences settings so that the tab based Preferences setting would be used when accessing them from the Options menu.

After doing this I repeated the above proxy changes and again noted that the changes did not stick.

This confirmed for me that the issue is nothing to do with the settings or profiles on my original laptop where the issue first occurred.

Next I completely uninstalled Firefox 28 and all user data and rebooted the laptop. I then downloaded and installed the current nightly version of Firefox (31.0a1 2014-04-02) and rebooted the laptop.

I then repeated the exact same procedure as above and the results were identical. That is, proxy setting changes using the tab based Preferences would not stick.

As I conducted these tests on a different laptop with a clean Windows User account and clean installations of both Firefox 28 and Nightly I believe the issue is a bug in Firefox tab based Preferences and I will be reporting it as such.

Whilst we know that a bug on one system may not necessarily be a bug or an issue on another system, in my case it was.