openSUSE has per default installation a Firefox extension which is thought to integrate the browser better into the distribution. However, this extension is no longer compatible to Firefox 6 (which is in Tumbleweed, but meanwhile also in the update repo for 11.4 standard). Looking at the extension’s homepages (OpenSUSE Firefox extension - openSUSE, susefox in openSUSE - Gitorious), it looks as if there is no more activity in this project. The functionality seems to be reduced to a simple plugin finder (I remember that in former times openSUSE had some more features to integrate Firefox e.g. in KDE).
Is this extension deprecated?
It’s future is unclear. However, if you ever need to run any extension on a newer version of Firefox, you should try an extension called “Nightly tester tools”. It allows to bypass version checking for other extensions.
This warning message is harmless and can be ignored.
Once they have a working openSUSE FF extension they will publish it.
It is true that the warning message (along with the disabling of “openSUSE Firefox Extensions”) is harmless, if one is running the Firefox “Nightly Tester Tools” (see openSUSE Firefox extensions not compatible with Firefox 6.0) or has installed the “Add-On Compatibility Reporter” Firefox extension (see Firefox 6 Cookies - Page 2), then the presence of the downlevel “openSUSE Firefox Extensions” may have unwanted or deleterious effects.
In the second link (above), I noted that one can replace the “MozillaFirefox-branding-openSUSE” package with “MozillaFirefox-branding-upstream” to remove the undesirable extension. As an alternative, one may manually disable the extension. Simple removal from Firefox will not resolve the problem, as Firefox will automatically re-install the downlevel extension at the next startup.