Could you give me a little more information on your experience in Firefox's Safe Mode? Was Amazon working correctly in Safe Mode or did the problem continue?

To further investigate the mystery button:

• If you hover your mouse over it, is there any tooltip that indicates its function?

• If you use Firefox's Customize feature and drag if off the toolbar to where the other unused buttons rest, is there a name listed under it that might help track down the source?

Also, could you review your recent installs in case this snuck in as part of a bundle? Windows Control Panel, Uninstall a Program, click the "Installed on" column heading to sort by date.

Also, in case you haven't already:

When you have a problem with one particular site, a good "first thing to try" is clearing your Firefox cache and deleting your saved cookies for the site.

(1) Bypass Firefox's Cache

Use Ctrl+Shift+r to reload the page fresh from the server.

Alternately, you also can clear Firefox's cache completely using:

"3-bar" menu button (or Tools menu) > Options > Advanced

On the Network mini-tab > Cached Web Content : "Clear Now"

If you have a large hard drive, this might take a few minutes.

(2) Remove the site's cookies (save any pending work first). While viewing a page on the site, try either:

• right-click and choose View Page Info > Security > "View Cookies"
• Alt+t (open the classic Tools menu) > Page Info > Security > "View Cookies"

In the dialog that opens, you can remove the site's cookies individually.

Then try reloading the page. Does that help?

The problem persists in Safe Mode--I just retested that idea.

Tool tip occurs on hover? No.
Drag & drop in 'customize' on? No. 

Rt clk reveals greyed-out: move to menu and remove from toolbar. Control Panel, 'Programs install/uninstall: no installs since March, which predates this problem by almost two months. I have earlier cleared the cache and 'everything else': history and such. Problem persists. I shall revisit these and check out the ideas you suggest. Grateful for your timely reply!

In general, all of these ideas have been tested. 1. When you have a problem with one particular site, a good "first thing to try" is clearing your Firefox cache and deleting your saved cookies for the site. DONE. 2. Use Ctrl+Shift+r to reload the page fresh from the server. DONE. This includes re-logging-in to the site, selecting a book and checking to see if the 'buy button' appears. It actually a colorful dialogue box. It does not appear--at all. Like most of FF webpages these days, all color is bled-out. 3. On the Network mini-tab > Cached Web Content : "Clear Now" DONE. 4. (2) Remove the site's cookies (save any pending work first). While viewing a page on the site, try either: DONE. This included remove one cookie, reloading the pate and re-testing for a purchase. No buy dialogue box appears. 5. Removal of either a single cookie or all cookies : Amazon restored them. I DID NOT repeat step (4) above for each and every single cookie (Is that recommended? ) --only for two or three and Amz immediately reloaded them. 6.BTW. It seems to me that, earlier in the day--this has been a day's-long project) that I reloaded FF at least once. But that , it appears, is not the same as removing and reinstalling. Is that recommended? I am prepared to do that: it seems that this is a malware FF toolbar hijacking. Please point to the pages where these instructions are to be found---fatigue sets in. Thanks!

Color bled-out on most pages? Two thoughts:

(1) I assume you have confirmed in the Options dialog that you are allowing pages to use their specified colors and styles. That's here:

"3-bar" menu button (or Tools menu) > Options > Content > "Colors" button > Allow pages to choose their own colors

(2) Some users get missing colors and images when there are issues with security certificates. Have you noticed an uptick in errors relating to secure sites? Have you added any "exceptions" for those sites?

This was successful! Thanks. The earlier problem involving the 'hijacked'??? toolbar, remains. It is worrisome as the '3bar menu button' temporarily was disabled. In addition, IE is now malfunctioning and the Start/Taskbar settings have become unstable. "3-bar" menu button (or Tools menu) > Options > Content > "Colors" button > Allow pages to choose their own colors

The 'colors' solution above also solved the Amazon problem---to a degree. The 'buy' button now stands out more clearly but only the 'gift' option is clear. I guessed at the functionality of the 'buy' option/button and tested it successfully. THANKS!!!!!

 The vexatious and worrying 'flag button' on the rt end of the FF toolbar remains.

Could you post a small screenshot showing the button? Perhaps someone will recognize it and be able to tell you which extension it belongs to.

This article has tips: How do I create a screenshot of my problem?

Yes but it is a bit small. How to enlarge before posting? Many, many thanks for your kind, patient and tactful assistance!!!!!

My guess would be it is related to bookmarks or favorites...

Maybe Add to Wunderlist:

Maybe the gray appearance on the toolbar means it isn't currently connected to the mother ship?

You are certainly right! I elected the Wunderlist add-on but it has not been activated---there is no account. Hence, I did not believe that further actions by me were indicated. Wrong! This has been a bad day for stupid oversights. Many thanks.

No worries. I'm glad it wasn't malware!