Computer has been doing funny stuff since I went to Firefox...
You must be new to Firefox. You probably, unknowingly, were in a private window/tab. When you close a private window/tab, all traces of any page(s) you visited (while in that window/tab) are removed from your computer. It's a nice feature, but when you forget or don't realize you're in private browsing...well, you know the rest of the story.
Here are 2 signs that you are in private browsing:
- The page title (on the tab button) will be underscored with a semi-dotted line.
- To the far right of FF's menu bar, there will be a small purple box with a masquerade style mask (certain customizations to FF's menu bar may make this box not visible.)
FF, by default, allows you to open a private window in which all tabs opened will be private. There is an Add-On that lets you open private tabs within any window. It will give you a masquerade looking button which you can drag to your menu bar which opens a private tab. Let me know if you need any help finding/dragging the button. Here is the link to the "Private Tabs" Add-On:
https://addons.mozilla.org/en-US/firefox/addon/private-tab/?src=api