Rated 5 out of 5 stars

This addon is amazing. I agree with the developer that it is the best search extension available in various popular browsers. (With that, I can simply remove several search addons....)

Here are some suggestions to make the addon even more awesome:

It is better if it has the following features:
1. an option to set the size of "search panel" launched by ctrl+shift+f
2. an option to set url bar instant search to only load history/bookmark, but not to query and load any suggestions from search engine
3. an option to set search engine instant search based on what user has typed in real time (with a time delay value to specify) but not to make query for and based on the search engine suggestions
4. conduct site search of current web page using google, allowing user to specify query before googling.

[The content below is edited after developer's first feedback on 25 Dec 2011]

First, okay ... already changed the rating to 5 stars to reflect the huge capability possessed by such addon.

For suggestion 1, because I find that the findbar may not fit well if we have installed some stylesheet using stylish (e.g. scrollbar modification), so allowing the bar to freely resize and remembering the setting may help for the case. I believe this case may occur if some users use themes rather than default theme as well.

For suggestion 2 & 3: this may fit well for those privacy-concern users (some may not want a work-in-progress query to be sent out for search suggestion from google when searching in other engines), or those less relying on search suggestion (like me)

For suggestion 4: yes I mean that capability exactly. I believe a top search addon should have this implemented and can be executed with ease, in which your addon does very well in such aspect. This is a must considering the poor accuracy of most sites' search function .... (will try this function later) Such great capability is better to be documented for users' reference as well.

[update 2 on 27 Dec 2011]
For suggestion 1, the best solution I can think of is the same as the one you suggest, an option to set the width/height of the search panel.

BTW, if you hope more people will find your addon, I suggest you opening a thread in the forum of mozillazine. Generally, there are many power users there, and they may also contribute great ideas for your addon as well. It may serve as your "support forum" as well.

This review is for a previous version of the add-on (1.98.1-signed). 

Thanks for the mozillazine suggestion. I'll try it out later.

To answer your suggestions:
1. <b>Update</b>: In v2.01 and above, there's now an option in "Text Search Settings" that switches to a much smaller text search panel when you press Ctrl-Shift-F.
2&3. <b>Update</b>: It's done in v2.01 in the "Instant Settings". The Options are named "Search only what you typed" and in the following section titled "Instant uses search results from", where you can choose to search both history/bookmark and engine, or just engine, or just history/bookmark.<br>Download v2.01 from https://addons.mozilla.org/en-US/firefox/addon/fastest-search/versions/
4. If I understand you correctly, this feature was already implemented in v1.89 but undocumented. Basically just set the query string for a search engine to sth. like http://www.google.com/search?q=DO_NOT_CHANGE_THIS site:DO_NOT_CHANGE_THIS_DOM&amp;amp;amp;amp;ie=utf-8&amp;amp;amp;amp;oe=utf-8&amp;amp;amp;amp;aq=t&amp;amp;amp;amp;rls=org.mozilla:en-US:official&amp;amp;amp;amp;client=firefox-a, then do the search using the engine, you'll see the domain for current page auto-inserted so that your search on the selected keyword on current page is only done on the current page's domain (say, page is http://subdomain.domain.com/abc.html, then domain is domain.com). You can also use DO_NOT_CHANGE_THIS_SUBDOM, DO_NOT_CHANGE_THIS_TLD, DO_NOT_CHANGE_THIS_URL for subdomain of current page (subdomain.domain.com), top-level-domain (.com), or exact URL (added just in case a user needs, not useful for site search). So all you need to do is make another engine(s) that uses the URL(s) above to do site search.