Rated 5 out of 5 stars

Tested 2.8.2, both bugs are fixed, partial compatibility with Private Tab is now granted.
Why partial? Because there's one issue - that I don't whether you left it so intntionally (and it makes sense, since that's just a matter of taste) or just didn't notice and would like to fix it (or not):
add-on Private Tab adds a Ctrl+Alt+V hotkey (and optionally a menuitem to tabs' context menu) to open a non-private tab, even in a private window (which is forbidden in Firefox by default) + allows users to drag'n'drop a non-private tab to the private window.
And your extension currently opens a private tab from a non-private one, if it is in a private window.
That's not a bug, but just a matter of personal preferences, I guess.
+ I don't use private windows, so personally I don't care about this at all.

I'm almost fully satisfied with InstantFox, however I have one feature request, that I actually requested earlier by email, but got no response.
I like a feature that appeared in IE since v.9 (and is present in v.10 too): when you type something in the address bar - a dropdown list appears with history and/or web search results, but IE9 has a small toolbar that consists of search engines' favicons, so user could quickly search for something using the selected engine.
http://storage1.static.itmages.ru/i/13/0418/h_1366282650_9485887_90af8c6366.png
This might be useful for some user with short memory, so they don't have to remember keywords for search engines. Or for the users that sometimes forget rarely used search engines. Or for the users that like mouse more than keyboard.
In IE - that toolbar is configurable, so users can select what search engines to put there.
I really would like to see that in InstantFox.
Anyways, thanks for your awesome extension! Finally can use it again!

This review is for a previous version of the add-on (2.8.0). 

interesting feature request! I not sure if it fits to Instantfox or if it might me an extra add-on or option. I like the idea of helping user with a short memory, may be one can add the "most-or-last-used-by-user" searchengines there. Feel free to add it to our issue tracker.

Just a hint, we need to be very careful with more features, some addons get cluttered quickly: https://addons.mozilla.org/en-US/firefox/addon/instantfox/reviews/451270/ < i like to keep it simple and stupid (it's already much more)

I appreciate your bugfix a lot! Rated 5 out of 5 stars

Thanks that you didn't treat me like a troll or something, I'm really interested in your add-on, I just couldn't live with that bug, and now you've finally fixed it, thanks a lot!
My github name is the same as here. That's really awesome that you realize now how important to have an open issue tracker for any project, especially open one.
However, I've found a bug/regression in the version you suggested: if you type "g something" into the address bar, then hit Ctrl+A to select everything in the address bar and then hit "delete" - nothing actually happens.
Expected result is that it would erase all the text typed into the address bar.

And since now stable version of Firefox has private windows, could you take a look into that review of another extension, but that is actually related to yours?
https://addons.mozilla.org/en-US/firefox/addon/private-tab/reviews/451236/

This review is for a previous version of the add-on (2.8.0). 

already tested, before i replied :) - Chapeau and thank you for your help

I just added you to our private issue tracker, feel free to participate. I'll try to add a public one, soon!

You don't use public issue tracker Rated 5 out of 5 stars

1. Users may change their marks and they can leave multiple reviews, but only last review gets counted, so if I downvote you 100 times and then upvote once - you'll get only the upvote from me, so don't be disappointed much, that's fixable ;-)
2. This site doesn't provide a way for a user to leave a reply to developer's comment, so a developers unfairly hold users at the vantage. The site makes me leave extra reviews.
3. If you had, say, a repo on github - we'd discuss issues there, without reviews. But you don't have an issue tracker.
4. Many developers don't even read comments with 5 stars, because it basically means, that the user is contented with everything. The thing is I don't, that's why my last reviews are negative [you ignored my very first review, which had a 5-start rating, which just proves my point].
That is exactly why I asked you to create a github repo (it's not even necessary to upload your code there, you could just use it to track issues). Please, reconsider this.
And don't take any offense at me.

Now to the issue:
Are you talking about this feature?
http://storage8.static.itmages.ru/i/13/0411/h_1365680899_5037487_492c9672e2.png
I switched it off, but it didn't change anything, I still see InstantFox' injections into the dropdown list when I type-in anything into address bar:
http://storage9.static.itmages.ru/i/13/0411/h_1365680981_7970243_8265a2ee95.png

This review is for a previous version of the add-on (2.8.0). 

true points + thank you for your helpful bugreports and feedback.

The issue should be fixed right here:
https://addons.mozilla.org/en-us/firefox/addon/instantfox/versions/#version-2.8.1

I just put on my ToDo to clean up our Github issue tracker to open it up for the public.
In the meantime you are welcome to drop me your Github name.

Please, fix the bug Rated 5 out of 5 stars

When Instant Fox is enabled - pref "browser.search.defaultenginename" gets ignored.Edit: thanks for fixing.

This review is for a previous version of the add-on (2.7.1). 

thank you, i'll put this on our issue list