Hi bluecap, could you describe what you mean by "after I leave them" in more detail? For example, does the problem occur when:

• you follow a link (go forward) in the same tab, and when you click the back button the previous page is blank?
• you launch a new tab (Ctrl+t) or follow a link in a new tab, and when you close the new tab or click the previous tab, the previous tab is blank?

Is there any pattern to the site that needs to be reloaded, or does this happen on every site?

In case it happens on sites that refresh themselves with new content by reloading the page from time to time, could you make sure the reload block is not turned on? You can do that here:

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

In the left column, click Advanced. On the right side, with the "General" mini-tab active, uncheck the box for "Warn me when websites try to redirect or reload the page" if it is checked.

In case you haven't recently, could you clear Firefox's cache completely?

See: How to clear the Firefox cache

If you have a large hard drive, this might take a few minutes. If you do not see the number going down on the page, you can reload it using Ctrl+r to check progress.

Oh... if you meant this:

When you exit out of Firefox and start it back up and restore your previous session windows and tabs, you were used to having them all load immediately rather than "on demand" as you visited them:

I think the default was reinstated as part of the transition to "e10s," a major internal change in how Firefox works. That setting doubles or triples the startup time with the new separation of content from browser interface.

But feel free to try it and see what you think:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful.

(2) In the search box above the list, type or paste sess and pause while the list is filtered

(3) Double-click the browser.sessionstore.restore_on_demand preference to switch the value from true to false

But I wonder: is there a more general problem of tabs loading slowly now, whether they are old tabs or new tabs?

Thanks for responding. More details:

The situation is very simple, if I merely go to another Tab (whether opening a new Link/Tab or going to one previously opened) the page/Tab is blank and in the process of reloading which invariably takes much time...unlike when a site that I may be at is refreshing.

There is no pattern it occurs on every single Tab/Page regardless of the site or how many Tabs I may have open at the time.

The Reload block is not enabled and never has been.

There is no issue with Restarting Firefox or Restoring.

A session runs fine for a short time, sometimes longer than others, then "all Tabs/Pages go blank" that I am not currently on when I navigate back to them....all Tabs....even the one I was on when I then go back to it.

I have not heard of that one before.

One of the headline changes in Firefox 48+ is e10s, which separates the browser interface process from the page content process. The performance impact of this can vary a lot between systems, so could you check whether you have this feature turned on? Either:

• "3-bar" menu button > "?" button > Troubleshooting Information
• (menu bar) Help > Troubleshooting Information
• type or paste about:support in the address bar and press Enter

In the first table on the page, check the row for "Multiprocess Windows" and see whether the number on the left side of the fraction is greater than zero. If so, you are using e10s.

To help evaluate whether that is causing this problem, you could turn it off as follows:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful.

(2) In the search box above the list, type or paste autos and pause while the list is filtered

(3) Double-click the browser.tabs.remote.autostart.2 preference to switch the value from true to false

Note: the exact name of the preference may vary, but it will start with browser.tabs.remote.autostart

At your next Firefox startup, it should run in the traditional way. Any difference?

On this Troubleshooting Information page I do not see," In the search box above the list"....there is no Search Bar on this page at all.

However, as I did not experience this anomaly in the 4 previous updates since 48.0 (I am on 49.0.2) I suspect this is not the issue.

However, back to potential "site triggers" of the issue.

Since I surf different sites and sources fairly prolifically, I am thinking that maybe in fact a new site I started accessing that happened to coincide with the Firefox update is a possibility.....some kind of Malware that has squeaked by Kaspersky???

I guess this is possible.

I think I will limit my browsing to nothing but the "old" sites for a day and see what happens.

Hi bluecap, I was referring to two different pages. I'll put a divider into my post to clarify that, sorry.

With respect to Kaspersky, there are two features which may affect how pages load in Firefox. One is a general filter on all web traffic, and another is "Anti-Banner" which can substitute a one pixel image for advertising content. An update could have affected how those work; I haven't been reading up on it.