The Reset Firefox feature can fix many issues by restoring Firefox to its factory default state while saving your essential information. Note: This will cause you to lose any Extensions, Open websites, and some Preferences.

To Reset Firefox do the following:

1. Go to Firefox > Help > Troubleshooting Information.
2. Click the "Reset Firefox" button.
3. Firefox will close and reset. After Firefox is done, it will show a window with the information that is imported. Click Finish.
4. Firefox will open with all factory defaults applied.

Further information can be found in the Refresh Firefox - reset add-ons and settings article.

Did this fix your problems? Please report back to us!

Thanks.

I've seen that solution. However, this would entail reinstalling all bookmarks, extensions, addons etc. surely?

Rather a long-winded process for an upgrade that in the past has 'just worked', and it's one I'm loathe to carry out at the minute as I don't have the time nor patience to do this process on the two machines that are having issues.

And even after adding everything back there's no guarantee that it will work as intended.

Frustrated

I agree. Though I've heard the Reset feature will automatically copy over bookmarks, passwords, web history, cookies and form history BUT not addons and addon related settings or any currently open tabs, download history, custom exceptions lists (like for cookies, etc) and more. I don't like this feature for these reasons both you & I mentioned. But in other cases where Firefox has been hijacked by malware or annoying toolbars, it can be a big help.

The full list of what is reset is here:
https://support.mozilla.org/en-US/kb/reset-firefox-easily-fix-most-problems

I have another idea though.

Could you check the Options area of Firefox? Earlier today a user reported to me that he was using Firefox on Mac and couldn't visit any websites. He then checked his proxy settings and found there was a incorrect setting there. He changed it to "No proxy" and everything started working again.

To change proxy settings:
Click the Firefox button > Options > Options
In the Options window, click Advanced > Network
Then in the section for Connection, click the Settings button.

Screenshot:

In the Connection Settings window that pops up, remember what setting is selected and in your next reply tell me what it was. Now choose No proxy then click OK. Now try to visit a website. If it still won't browse, close Firefox and open it again. If it doesn't work after this, I think a addon may be responsible.

You can also double check the steps I listed above in the article below, in case it is easier to understand.

Link:
https://support.mozilla.org/en-US/kb/firefox-cant-load-websites-other-browsers-can#w_firefox-connection-settings

Hi Noah.

Have tried all the related steps in Mozilla Support, including your proxy settings suggestion.

My first thought that it may be an addon, but shied away as at the time it appeared a tad labour intensive.

Looks like that will be my next step, so I may be gone some time

Thanks for the suggestions so far

Will return with my findings at some point

Herb

Okay, issue resolved

It was the 'leethax.net' extension causing it.

All back to normal now

Thanks all

Herb

And thank you! For painstakingly going thru and disabling your addons one by one until you found what was causing this problem. And for returning and letting us know what caused the problem (most just say: I fixed it! The end.). I feel your pain as I've had to do the same procedure many times myself. And when Firefox upgrades from one release to the next with yet again some crazy new problem that I have to investigate like Sherlock Holmes I do get angry! :D

Unfortunately addons break Firefox from time to time in between releases. Sometimes it's because the addon is super old and it just finally broke (like a car) and other times I blame the Firefox developers for too frequently introducing too much new code that breaks properly updated addons.

Anyway, we'll spread the word about the leethax.net addon and help other people who report the same problems you had. Thanks again.