Taskbar previews are not shown when there are more than 20 tabs across all Firefox windows unless tabs are in groups.
System details: Windows 8.1, Firefox 34.0.5. Until today, I have not used the Tab Groups function. Today I just used it in troubleshooting this issue.
I noticed that when I have lots of Firefox windows open, I can't see taskbar previews for all the open tabs. The taskbar previews only show the active tab for any specific Firefox window. After some investigation I found that if I have 20 or fewer tabs open (in one Firefox window or across multiple Firefox windows) I can see taskbar previews for all the tabs. More than 20 tabs and the taskbar previews change to show only the active tab for each Firefox window.
After a little more investigation I found that I can see more than 20 taskbar tab previews if I use the Tab Groups function. I don't need to actually organize my tabs into groups, just to invoke the Tab Group function in each window. Trouble is, the tab groups do not survive after closing Firefox. I think this is probably because of an extension I use called Session Manager. Since I am not ready to give up the extension, I wonder if I can change the taskbar preview behavior to show more than 20 tab previews in the taskbar without using the tab groups function.
Thanks in advance for any suggestions.
I am not entirely sure, but this menu should change that preview in your OS: Control Panel > Taskbar > Taskbar Properties > Jump Lists change the number from 10 to the number of tabs
If it doesn't please see Windows support for help.