It looks like an extension issue. Could you test the basic troubleshooting steps, please: 1)safe mode: https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode 2)new profile: https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles Does it fix the error message?
Paul, let me suggest going to http://support.mozilla.org/ . This is the best place to receive support on any issue you might encounter. Here, you are not on a forum, but on one of the tools used by the team developing Firefox to track and prioritize bugs and features, so you will certainly receive less help.
Loic, I have isolated the extension causing the error; it is the AustLII Toolbar which provides quick access to the Australian Legal Information Institute and search functionality right from the toolbar. I have had this extension for years and years, certainly going back to Firefox's early single digit versions. However, I have not previously had this error come up; it was only since updating from FF15 to FF18 that I noticed this error (which really interrupts web browsing) so it seems AustLII's toolabr is no longer fully compatible with Firefox. I have lodged a report through the Extensions tab. But thank you for your advice; I wouldn't have realised I had an "extension issue" but for your post. Many thanks.
Paul, which version of the toolbar are you using? I installed version 1.6 from their website and I haven't been able to reproduce this error. Given that it was updated relatively recently (November), I would presume that the error was fixed. If you can still reproduce the error with version 1.6 of the extension, please tell me which websites you see this on.
Jorge, I was using 1.5.0. I have updated to 1.6.0 and re-enabled the plugin and have not been able to reproduce the error. I note when I updated to FF18 only a few weeks ago it did the compatibility and update check for add-ons which it normally does but did not come up with an update for AustLII. As for the error itself, previously I was getting this error on just about every web page I navigated to, as well as the initial error upon launching the web browser.