This site will have limited functionality while we undergo maintenance to improve your experience. If an article doesn't solve your issue and you want to ask a question, we have our support community waiting to help you at @FirefoxSupport on Twitter and/r/firefox on Reddit.

Search Support

Avoid support scams. We will never ask you to call or text a phone number or share personal information. Please report suspicious activity using the “Report Abuse” option.

Learn More

Recently, whenever I try to open Firefox, I get a dialog box: Exc in ev handl: TypeError: brw is undefined (JavaScript Application). Firefox is definitely my default browser

more options

Question Recently, whenever I try to open Firefox, I get a dialog box: Exc in ev handl: TypeError: brw is undefined (JavaScript Application). Firefox is definitely my default browser. After clicking OK Firefox opens.

Question Recently, whenever I try to open Firefox, I get a dialog box: Exc in ev handl: TypeError: brw is undefined (JavaScript Application). Firefox is definitely my default browser. After clicking OK Firefox opens.

Chosen solution

You can probably get rid of it by disabling McAfee Site Advisor ending Firefox and then restarting Firefox, and re-enabling McAfee Site Advisor, ending Firefox and restarting Firefox. But it would probably be better to uninstall Site Advisor and reinstall (as opposed to the update)...

Please see solution in http://kb.mozillazine.org/Problematic_extensions for "McAfee Site Advisor".

(Windows): For best results you should uninstall McAfee Site Advisor from Control Panel > add/change programs (Programs and Features). Reboot the system. Then Reinstall from http://www.siteadvisor.com/ and reboot the system. When installing refuse other suggested (crapware) applications.


Please mark "Solved" one answer that will best help others with a similar problem -- hope this was it.

Read this answer in context 👍 0

All Replies (4)

more options

Seçilmiş Həll

You can probably get rid of it by disabling McAfee Site Advisor ending Firefox and then restarting Firefox, and re-enabling McAfee Site Advisor, ending Firefox and restarting Firefox. But it would probably be better to uninstall Site Advisor and reinstall (as opposed to the update)...

Please see solution in http://kb.mozillazine.org/Problematic_extensions for "McAfee Site Advisor".

(Windows): For best results you should uninstall McAfee Site Advisor from Control Panel > add/change programs (Programs and Features). Reboot the system. Then Reinstall from http://www.siteadvisor.com/ and reboot the system. When installing refuse other suggested (crapware) applications.


Please mark "Solved" one answer that will best help others with a similar problem -- hope this was it.

more options

Thanks for this. I uninstalled McAfee SA then restarted. No problem. Then I reinstalled MSA and the problem reoccurred so I have uninstalled McAfee SA again and so far things are fine. It may be conflicting with something else.

more options

Doesn't work out for me either, so I keep it disabled, because it slows down the searches, and it won't stream its additions onto the pages after the first page of search results. Streaming or page zipping allows me to scroll down to the next page of search results without selecting the page number.

more options

This advice is extremely helpful. I had no clue to the solution of this problem. The only solution that I could think of was to uninstall FireFox and permanently from my computor. Thank You!