Roughly a month and a half since issuing its last major update, Mozilla has begun a campaign aimed at encouraging users of Firefox 3.0 to move on to the newest version. According to an official blog post, starting this past weekend an update offer in the form of a popup is presenting users with the option of downloading Firefox 3.5 immediately, postponing for 24 hours or declining the update altogether. Previously, in order to stumble upon the new version, Firefox 3.0 users needed to specifically search for updates.

Mozilla touts better performance in version 3.5 along with features like private browsing and tear-off tabs. However, it also warns users of potential add-on incompatibilities – which could be a deal breaker for many. We recently posted a workaround to get incompatible add-ons running with the latest version of Firefox, but there are no guarantees that they’ll function properly and in fact results can vary considerably.

Firefox 3.0.x is still going to be supported until the end of the year. At that time, Mozilla will halt production of security patches for the older version, forcing any remaining holdouts to finally upgrade.