I don't think "oh snap" is a built-in Firefox error message. Perhaps this is a message displayed by one of Google's scripts when there is a problem in the page. Do you get the "Gah!" your tab crashed message??

Anyway, let's see whether we can track it down.

First, if you haven't already, could you close out of Firefox and do a normal Windows shutdown and restart to complete any pending updates and release any file locks.

Downloadable Fonts

Note: this is for pages on the web (http: or https:) and not local (file:). For local file issues, see: https://support.mozilla.org/questions/1264603

Here are a couple things to check, the details follow:

(1) Font setting -- are pages allowed to specify fonts to use? (2) Is a setting or add-on blocking downloadable fonts?

For #1, go to the Options page:

• Windows: "3-bar" menu button (or Tools menu) > Options
• Mac: "3-bar" menu button (or Firefox menu) > Preferences
• 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, scroll down to the "Fonts & Colors" section and click the "Advanced" button.

Then make sure the box is checked for "Allow pages to choose their own fonts, instead of your selections above":

Any difference (you would need to reload the problem page, Ctrl+r or the circling arrow button, to see any difference)?

For #2, some add-ons have a feature to globally block downloadable fonts unless you specially allow them. Do you run uBlock Origin or NoScript, for example? In uBlock Origin, the setting is called "Block remote fonts".

There's also a general setting to block downloadable fonts in about:config, if you think you might ever have changed that:

(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 or accepting the risk.

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

(3) If the gfx.downloadable_fonts.enabled preference is bolded and "modified" or "user set" to false, double-click it to restore the default value of true

Was it any of those things?

Bookmark/History Check

Could you let us know what you get when you run the "Verify Integrity" function. That's here:

Open Firefox's Troubleshooting Information page using any of these methods:

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

Near the bottom, there is a section titled Places Database -- that's the file which stores history and bookmarks. Click the button labeled Verify Integrity. There may be a 10-15 second delay before results appear.

If all is well, the report that appears below the button should start with:

> Task: checkIntegrity
+ The places.sqlite database is sane
+ The favicons.sqlite database is sane

Does yours say that, or something else? You can select and copy the report, and then paste it into a reply for review and comment.

You can create a new profile to test if your current profile is causing the problem.

See "Creating a profile":

• https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues

If the new profile works then you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over problems.

• https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

You can copy files like these with Firefox closed to the current profile folder to recover specific data. Note that you should be cautious with copying SQLite database files if you previously had problems.

• bookmarks and history: places.sqlite
• bookmark backups: compressed .jsonlz4 JSON backups in the bookmarkbackups folder
• cookies.sqlite for the Cookies
• formhistory.sqlite for saved autocomplete Form Data
• logins.json (passwords) and key4.db (58+) or key3.db (57 and older) (decryption key) for Passwords saved in the Password Manager
  if you only have key3.db then make sure to remove an existing key4.db
• cert9.db (58+) or cert8.db (57 and older) for (intermediate) certificates stored in the Certificate Manager
  if you only have cert8.db then make sure to remove an existing cert9.db
• persdict.dat for words you added to the spelling checker dictionary
• permissions.sqlite for Permissions and possibly content-prefs.sqlite for other website specific data (Site Preferences)
• sessionstore.jsonlz4 for open tabs and pinned tabs (see also the sessionstore-backups folder)

See also:

• https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

thank you for a high quality response - I learned things from parts of your response that I did not know. my opening remark was snarky - the error message (oh snap) was a google message, not a FF message however, I am not having a problem with declaring (CSS) and using google fonts. my problem is that the google font page crashes after 12-14 seconds. that specific page is handled properly in Chrome, Brave and Edge. Furthermore, the Google Fonts page is handled as expected on FF-mobile.

WRT your response and #1, attached is:

 2019-09-28_5-09-13_-_fonts-enabled_.jpg

WRT Places Database, attached is:

 2019-09-28_5-12-49_-_places-database_.jpg

I've also attached a screen shot of the Google Developer site that shows how the Font Awesome icons are handled:

 2019-09-28_5-05-23_-_google-developer-site_.jpg

I am reluctant to create a new profile and migrate existing bookmarks. I have exported my bookmarks to a JSON file and then imported them. IMHO that would clean up any corrupt data, unless you tell me differently.

Progress: I've checked the main points of your response, but

 FF does not display Font Awesome fonts on the Google Developer site ONLY
   FF does properly display Font Awesome fonts on other sites
 the Google Fonts page breaks after 12-14 seconds.
   I launch the page and do nothing (no clicks) for 12-14 seconds and then breaks

When raising these issues in the past, I was advised to change the security setting to the most permissive level and to turn off extensions such as ad blockers. So, to repeat from my initial submission, I am not running any extensions and Browser Privacy is Standard.

I will follow additional instructions and provide additional information per your request. But I would prefer not to follow the profile migration. I'll live with the current issues if non-profile-migration solutions fail.

/jay

Here is the third image /j

Update: I did a Firefox refresh

 Google Developer Font Awesome icons are handled correctly
 Google Font page does not crash

So thank you and Mozilla for self-service repair.

The open issue is:

 what caused the reported problem(s)

If it would help Mozilla, I can provide the 'before' and 'after' data to help identify the source of the error

Aside: The main reason I use and stay with FF is the bookmark manager

 it is the BEST

Chrome bookmarking, even with extensions, falls short of FF features

I do use Chrome for three reasons:

 1 the developer console
 2 there are applications that use services that run only in Chrome
 3 there are CSS features that run only in Chrome

I can provide examples of Chrome-only pages for Mozilla to review, if it would be helpful

Also, there are several add-ons that IMHO behave better in Chrome than FF I can provide examples with comments

Thank you again for your quality advice in helping me solve my problem

/jay gray

Hi Jay, thank you for reporting back.

Regarding before and after, you could do a text compare of the prefs.js file in your old profile folder (in the Old Firefox Data folder on the desktop) with the one in your current profile folder. A lot of the differences are runtime data, but others may be user-specified preferences.

I can provide examples of Chrome-only pages for Mozilla to review, if it would be helpful

Do you mean pages that prohibit other browsers, or pages that perform badly in other browsers? If pages are buggy, you can search/report on this site:

https://webcompat.com/

Also, there are several add-ons that IMHO behave better in Chrome than FF

If it's the same author/extension, they probably are aware of that problem. If it's a different, less full featured or less performant extension in Firefox, maybe the author of the Chrome extension can be persuaded to port the better extension. This is a little beyond the scope of the support forum. The Add-ons team has some forums where you could mention more details:

https://discourse.mozilla.org/c/add-ons

Thanks again for the on-target response. FF customer support differentiates FF from alternative browser support resources (although the Brave support forum is good).

I revisited all FF bookmarks that had problems (i.e. behaved differently from Chrome, Brave and Edge). All problems were resolved with the 'refresh'!

Being a long time FF user, I have made many small configuration changes over time. Clearly, one or more of those changes was the source of my problem. I need to go back and follow your advice to isolate those changes. I'll report back what I find for the benefit of others on this forum.

/jay