has greater functionality in this area. In turn, the Session Manager extension has additional session management functions beyond those of Tab Mix Plus. These two extensions are known to "play nicely together": Tab Mix Plus detects the presence of Session Manager and deactivates its own session management functions, deferring to Session Manager. Criticism Critics point out that TMP is quite large and may be experiencing software bloat. Versions Two versions of Tab Mix Plus are generally available at any given time: An "official release" version Intended for general use, this is publicly available from the Mozilla Add-ons website. These releases have passed the Mozilla Add-ons review process. A "development" or "pre-release" version Intended for testing by interested users prior to release, this is available only from the developers' own website. Firefox version compatibility Versions of Tab Mix Plus are available for virtually all releases of Firefox prior to Firefox 57. The release of Firefox 57 Quantum marked the switchover from XUL-based AddOns—which allow extensions to make arbitrary changes to Firefox code—to the WebExtensions API, which strictly limits how much control extensions have over the browser and interface. Because the original Tab Mix Plus is a XUL-based extension, it does not work with Firefox 57 or higher. A complete rewrite of the extension, called Tab Mix WebExtension, is in progress, and a development build with limited functionality has been released. See also List of Firefox extensions References External links Tab Mix Plus official homepage Tab Mix Plus Palemoon and Firefox Tab Mix Plus User Manual Tab Mix Plus at Mozilla Addons Free Firefox legacy extensions Pale Moon extensions