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I wanted to install a new add-on in Firefox – Firesheep, but when I tried to do so (from an xpi file), it told me that it can be installed because it's incompatible for 4.0.1.

However, compatibility check is disabled. Is there any way to force the add-on to install?

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as I said, compatibility check is disabled. (same way) – genesis Jun 24 '11 at 21:35
I know, that's why I said "related" and not "duplicate" :) – slhck Jun 24 '11 at 21:36
okay, thanks :) – genesis Jun 24 '11 at 21:38
Have you discovered an answer? I am having the same issue, I am using the add-on compatibility reporter yet I cannot get an add-on to install... – L84 Sep 30 '11 at 20:47
up vote 0 down vote accepted

You can use Add-on Compatibility Reporter. With this extension Firefox will install all extensions whether they are compatible or not. Additionally from the Addons Manager you can report (if you want) if a given extension is incompatible with the current version of Firefox or report bugs.

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Thanks. However, it didn't work out. It just showed the same thing as before (maybe because that add-on does not check installs from files?), however I can't find Firesheep anywhere in official add-on database – genesis Jun 25 '11 at 0:42
With this you just can force Firefox to install any extension, but not to force the compatibility. – Realcool Jul 18 '11 at 16:46
This doesn't work since firefox 10. – naught101 May 7 '12 at 0:13

As far as I'm concerned you can "hack" an xpi file to change the maximum version required.

  1. Rename the xpi to zip and extract it with your favorite unarchiving software
  2. Find the install.rdf file and open it in a text editor
  3. Change the following line (if you're talking about this Firesheep):

  4. to that one:

  5. Save the file and zip the whole folder again.

  6. Rename the zip into xpi and try to install the add-on again.

Note that this does not necessarily make the add-on work, but it should at least install.

share|improve this answer
I tried to change that too, I changed that to 5.0.* – genesis Jun 24 '11 at 21:37
Hm, should have mentioned in your question then! :) I don't know, this has worked for me once. – slhck Jun 24 '11 at 21:39

If all else fails, here are some links to download previous versions of Firefox:

You'll probably want version 3.6:

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This is a very old version of Firefox, and the question itself is probably no longer relevant. – bwDraco Oct 11 '12 at 15:33

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