Is the problem that the new tab button does nothing, and Command+t does nothing?

Many users have discovered this problem (in Firefox 30 and higher) is caused by Conduit add-ons, such as a Conduit plugin and/or a "Community Toolbar" extension.

You can check for and disable extensions on the Add-ons page. Either:

• Command+Shift+a
• "3-bar" menu button (or Tools menu) > Add-ons

(1) In the left column, click Plugins. Set nonessential plugins to "Never Activate".

(2) In the left column, click Extensions. Then, if in doubt, disable.

Often a link will appear above at least one disabled extension to restart Firefox. You can complete your work on the tab and click one of the links as the last step.

Does that help with the "+" button? If so, could you name the specific plugin/extension that caused the problem?

I should say that we don't have a lot of experience with 10.10 so this could be a new 10.10 issue that didn't occur in earlier versions of OSX.

unable to still open new tab with + or command T. Only way to open new tab is to click on firefox help on the open menu and click ?

Thank you for reporting this: I filed a bug for more help and would recommend also following this bug for more updates or if they ask for more information.

Thank you jscher and johnchoy!

johnchoy, if you still see this problem when using a newer version of Firefox, please test and answer the items listed by jscher2000 at https://support.mozilla.org/en-US/questions/1026347#answer-642569

FWIW, the bug filed is https://bugzilla.mozilla.org/show_bug.cgi?id=1087059