The switching to another tab should not close another.

Start Firefox in Safe Mode {web Link} by holding down the <Shift>
(Mac=Options) key, and then starting Firefox. Is the problem still there?

Separate Issue; Your System Details shows;

Installed Plug-ins

Shockwave Flash 20.0 r0 Shockwave Flash 18.0 r0
Having more than one version of a program may cause issues. You must remove the older programs. Then get the current full installer.

Flash: Grab the uninstaller from here: Uninstall Flash Player | Windows Uninstall Flash Player | Mac

Then reinstall the latest version.

Flash Player Version 20.0.0.267
https://www.adobe.com/products/flashplayer/distribution3.html Note: Windows users should download the ‘’’active_x’’’ for “Internet Explorer,” and the ‘’’plugin’’’ for “Plugin-based browsers” (like Firefox).

Note: Windows 8 and Windows 10 have built in flash players and Adobe will cause a conflict.

Adobe still offers Flash 18.0.0.268 as its extended support release further down

Sounds that you have a broken extension.

If it works in Safe Mode and in normal mode with all extensions (Firefox menu button/Tools > Add-ons > Extensions) disabled then try to find which extension is causing it by enabling one extension at a time until the problem reappears.

Close and restart Firefox after each change via *"3-bar" menu button > Exit (Power button)

• Windows: File > Exit
• Mac: Firefox > Quit Firefox
• Linux: File > Quit

• Hold Ctrl (Mac: Command) and left-click or middle-click the Reload button in the location/address bar to open the current page in a new tab (i.e. duplicate the current tab).
• Duplicate a tab with its history by holding down the Ctrl key (Mac: Option key) and dragging the tab to a new position on the tab bar.

Many, many thanks to FredMcD and cor-el for your helpful replies!

Sorry I haven't got back to you sooner. I've been watching my tabs. After updating several plug-ins and disabling some new extensions, I haven't experienced any episodes of "Tabs Behaving Badly". [Knock on wood.]

I felt like a bit of a boob when I discovered two different versions of Shockwave Flash installed at the same time. I used the link above and downloaded the Flash Player Uninstaller. I now have the current version of Adobe Flash Player (20.0.0.267) installed.

Oddly though, I don't see Flash Player - of any version - listed on my plug-ins page. I do however see Shockwave Player 20.0.r0 - originally marked as "Ask To Activate" but now marked as "Always Activated" - and Shockwave Player 18.0.r0 - marked as Disabled AND Never Activated

I'll try to keep you posted on any further developments. If you would like more info, just say the word.

SpecterFan110557

Flash shows as Shockwave Flash plugin in "Add-ons > Plugins" (about:addons) and in the System Detail list. Shockwave for Director is a different plugin, so do not confuse the two. Se also the about:plugins page.

• https://support.mozilla.org/kb/using-flash-plugin-firefox
• https://support.mozilla.org/kb/Using+the+Shockwave+plugin+with+Firefox

I'm baaaccckkk...

Tabs are back to randomly closing. It seems worse than before.

This is what I did:

1. Opened Addons
2. Located Shockwave Flash 18.0 r0 (NOTE: There was an Update Now

       link on version 18.0 r0 as well)

1. Set it to: Never Activate
2. This caused Shockwave Flash 20.0 r0 to re-set to Never Activate as

       well

1. Set it to: Always Activate which re-set version 18.0 r0 again
2. Clicked on the Update link and this window opened:
3. Flash Player Plugin 18.0.0.204 to 18.0.0.232 (click-to-play) has

               been blocked for your protection. etc, etc,...

1. Navigated to Adobe Flash Player site and downloaded the following:
2. Adobe Flash Player (Shockwave Player) version 20.0.0.267 for the

               Firefox, Mozilla - NPAPI Browser and downloaded the file:

1. flashplayer20_ha_install.exe
2. Exited Firefox
3. Ran: uninstall_flash_player.exe
4. Installed: Adobe Flash Player (Shockwave Player) 20.0.0.267 above
5. Re-started Browser

Shockwave Flash 18.0 r0 and Shockwave Player 20.0.0.267 are both listed under about:plugins and on the Add-ons page. I can not seem to get rid of Shockwave Flash 18.0 r0. Why?? I also noticed an entry on the programs page for Adobe Shockwave Player 12.2.2.172. Firefox and the Uninstaller don't seem to have noticed it.

And the tabs still randomly disappear.

PS Something I forgot to mention – neither Shockwave Player 18.0 r0 nor 20.0 r0 were listed as "disabled" or "Never Activate". They were both listed as "Ask To Activate".

SpecterFan110557 said

I'm baaaccckkk... Tabs are back to randomly closing. It seems worse than before.

The multiple Flash Plugins shouldn't be affecting your Tabs randomly closing issue. As cor-el mentioned in his first response, that is probably an extension issue.

See this support article - https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode

Here's an update-

I have uninstalled, rebooted, re-installed, and re-booted Flash Player and Firefox so many times that I've literally lost count.

I don't know what else to do.

I give up.......

First, you Did Not follow the instructions on this issue. See https://support.mozilla.org/en-US/questions/1103553#answer-828699

Second, the Flash problem is a Separate Issue

FredMcD said

Start Firefox in Safe Mode {web Link} by holding down the <Shift>
(Mac=Options) key, and then starting Firefox. Is the problem still there?

My apologies, sir. I'm a bit wary regarding Firefox and "Safe Mode". I had a bad experience involving Firefox, Safe Mode, Extensions, and losing a great deal of material once so now I try to avoid it whenever possible. Plus, I've been rather stubbornly attacking this from a "Flash-oriented perspective". Add to this a nasty health issue and well....

Again......

My apologies.....

On a different note I believe I have resolved the annoying Flash issue. I was examining my "about:plugins" page that Shockwave Flash - version: 18.0.0.232 - had placed a plugin file in a game folder on a different drive. The file in question - should anyone else encounter this problem - was NPSWF32.dll. I removed/renamed it and uninstalled version 20.0.0.267. I re-installed Adobe Flash Player version 20.0.0.267.

Finally, for the benefit of others: I'm running Windows 7 64-bit OS and Firefox is 43.0.4. Adobe Flash Player version 20.0.0.267 is listed as Shockwave Flash 20.0 r0 on my Add-ons page and Adobe Flash Player 20 NPAPI in the "Programs and Features" window in my Windows 7 "Control Panel.

As of right now the tabs seem to be behaving but prior to this email they were still acting up . Upon further unwanted activity, I will follow your instructions despite my own reluctance. I'll keep you posted.

Thanks again for your help and patience,

SpecterFan110557

SpecterFan110557 said

My apologies, sir. I'm a bit wary regarding Firefox and "Safe Mode". I had a bad experience involving Firefox, Safe Mode, Extensions, and losing a great deal of material once

I think you are talkiing about the Refresh/Reset option.

Safe Mode is a troubleshooting mode that temporarily turns off hardware acceleration, resets some settings, and disables add-ons (extensions and themes). If the problem goes away, that tells us one thing. If it does not, that tells us something else.

Refresh Firefox {web link} is a LAST RESORT ! !

Refresh Firefox - reset add-ons and settings

If you're having problems with Firefox, refreshing it can help. The refresh feature fixes many issues by restoring Firefox to its default state while saving your essential information like bookmarks, passwords, and open tabs.

The problem I keep running into is that this tab problem is not constant - it happens when IT wants to happen. I can't make it happen. It could take days for a re-occurrence and then again it could happen right now.

But I can tell you this –

Just before I popped over to this tab to post this reply, I clicked a tab several tabs away (I was viewing the tab that was next to it - to its right to be precise.) It seemed to be trying to open but instead suddenly closed and I found myself back on the tab I was just on. I was forced to click on "Reopen the Last Closed Tab" to open it back up (that's the easiest way).

This is why I'm here now. (Still fresh in my mind and all that.)

SpecterFan110557

Make sure that you do not click the close X button on the tab accidentally if you select the tab. The close button may only show clearly when you hover the tab with the mouse.

Can you post your extensions list:

• https://support.mozilla.org/kb/Using+the+Troubleshooting+Information+page

Sorry I didn't get back to you right away.

I found the list and copied it into OpenOffice. I exported it to a pdf file. If you need it in a different format just let me know.

I'm not sure how to insert a pdf file here but I'll give it a try.

SpecterFan110557

P.S. Something I forgot: in reference to the subject concerning "Safe Mode" - I believe I was instructed to click on "Restart with Add-ons Disabled" on the "Help Menu" but in all fairness it was quite some time ago. I could be in error.

Troubleshooting Data_2016-01-22.pdf

You can upload the file to a website like pastebin if the file is too big to put in a reply.

• http://pastebin.mozilla.org

Open a text / word program and load the file. Left click once. Now <Control> A to highlight everything, then <Control> C to copy it.

Next have your browser go to; https://pastebin.mozilla.org. Paste <Control> P the content of the file in the window. Note: On the bottom, choose to save the file 30 days.

Now press Send. The page will reload. Copy the new web address, and post it here.

SpecterFan110557 said

Troubleshooting Data_2016-01-22.pdf

Example Domain This domain is established to be used for illustrative examples in documents. You may use this domain in examples without prior coordination or asking for permission.