Hi tom238, what happens when you try to load GMail

https://mail.google.com/mail/

Could you copy/paste the error you get, or is it just a blank page?

If a site is generally known to work in Firefox, these are standard suggestions to try when it stops working normally:

Double-check content blockers: Firefox's Tracking Protection feature and extensions that counter ads and tracking may break websites that weren't built to operate normally without the blocked components.

Do you see a shield icon toward the left end of the address bar, near the lock icon? More info on managing the Tracking Protection feature in this article: What happened to Tracking Protection?.

Extensions such as Adblock Plus, Blur, Disconnect, Ghostery, NoScript, Privacy Badger, uBlock Origin or uMatrix should provide toolbar buttons to manage blocked content in a page. There may or may not be a number on the icon indicating the number of blocked items; you may need to click the button to see what's going on and test whether you need to make an exception for this site.

Cache and Cookies: 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) Clear Firefox's Cache

See: How to clear the Firefox cache

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 (on Mac Ctrl+click) a blank area of the page and choose View Page Info > Security > "Clear Cookies and Site Data"
• (menu bar) Tools > Page Info > Security > "Clear Cookies and Site Data"
• click the padlock or "i" icon in the address bar, then the ">" button, then More Information, and finally the "Clear Cookies and Site Data" button

In the dialog that opens, you will see one or more matches to the current address so you can remove the site's cookies individually without affecting other sites.

Then try reloading the page. Does that help?

Testing in Firefox's Safe Mode: In its Safe Mode, Firefox temporarily deactivates extensions, hardware acceleration, and some other advanced features to help you assess whether these are causing the problem.

If Firefox is not running: Hold down the Shift key when starting Firefox. (On Mac, hold down the option/alt key instead of the Shift key.)

If Firefox is running: You can restart Firefox in Safe Mode using either:

• "3-bar" menu button > "?" Help > Restart with Add-ons Disabled
• (menu bar) Help menu > Restart with Add-ons Disabled

and OK the restart.

Both scenarios: A small dialog should appear. Click "Start in Safe Mode" (not Refresh).

Any improvement?

Tried all of the above; no change. Screenshot of message attached.

By any chance, do you use Bitdefender, or another security suite that sets itself up as a "man in the middle" of your web browsing connections? If you think that's possible, please take a look at the steps in the following article to see whether letting Firefox connect directly resolves the issue: How to troubleshoot security error codes on secure websites.

Nope. I have VirusBarrier installed but real-time scanning is turned off. NetBarrier is also turned off.

Further note: Apparently anything Google is affected. Trying to do a Google search (www.google.com) gives the same message.

Is there anything unusual about your Firefox's connection settings? You can check that here:

• Mac: "3-bar" menu button (or Firefox menu) > Preferences
• Windows: "3-bar" menu button (or Tools menu) > Options
• Linux: "3-bar" menu button (or Edit menu) > Preferences
• Any system: type or paste about:preferences into the address bar and press Enter/Return to load it

In the search box at the top of the page, type proxy and Firefox should filter to the "Settings" button, which you can click.

The default of "Use system proxy settings" piggybacks on your Windows/IE "LAN" setting. "Auto-detect" can lead to a flaky connection. You may want to try "No proxy".

Any difference?

Tried with "no proxy"; same result. Incidentally, I'm using a Mac. Thanks for all the suggestions, but I guess I'll just have to stick with Safari for accessing my gmail.

Firefox normally can connect to Google. There may be faster and slower parts, but not being able to connect, without any explanation, is very unusual. I don't have any more easy suggestions, so do what you have to do...

Again, many thanks for trying to help. As I said previously, it was working fine yesterday morning, but later in the day the problem arose. No software changes in between.

Are there adblocker installed? Or what other extensions do you have installed?

Extensions installed are 404 Bookmarks, History Cleaner, and uBlock Origin. Tried it with all disabled and also tried Firefox Safe Mode. No success.