Mozilla's biggest concern: Users running 2010's Firefox 3.6 have put off updating to Firefox 5 because the toolbar won't work with the newer version.

"We know that a large amount of [Firefox 3.6] users are not taking update offers to [Firefox] 5+ due to Google Toolbar incompatibility," the read.

Elsewhere, Mozilla called the toolbar's incompatibility with newer versions of Firefox "a top support issue."

Nearly a third of all Firefox users still run Firefox 3.6, according to the most recent statistics from Web metrics company StatCounter. Firefox 3.6's usage share is, in fact, more than double that of Firefox 4.

Mozilla highlighted two steps it wanted to take in an update to Firefox 3.6 that's currently scheduled to ship Aug. 16. "[We] need to support getting data out of the Toolbar," Mozilla's meeting notes read, "[and we] need to tell them the Toolbar is gone and not coming back."