Hi makingitbetter, I'm not sure how to track down the problem because it sounds random. If we had a clear idea of the source of the error it would be easier to believe that a fix could be developed. I think you might have to live with it for a bit and see whether you can spot a pattern.

You also could keep Firefox's Browser Console open in a separate window and when that dialog pops up, peek at the latest error messages to see whether anything looks helpful. More info on that tool:

https://developer.mozilla.org/docs/Tools/Browser_Console

Firefox's Browser Console will this help

Unknown property ‘-moz-osx-font-smoothing’. Declaration dropped. application.css:1:461 Unknown property ‘speak’. Declaration dropped. application.css:1:632 Error in parsing value for ‘font-style’. Skipped to next declaration. application.css:1:8589 Error in parsing value for ‘font-weight’. Skipped to next declaration. application.css:1:8610 Error in parsing value for ‘font-style’. Skipped to next declaration. application.css:1:8953 Error in parsing value for ‘font-weight’. Skipped to next declaration. application.css:1:8974 Error in parsing value for ‘font-style’. Skipped to next declaration. application.css:1:9319 Error in parsing value for ‘font-weight’. Skipped to next declaration. application.css:1:9340 Error in parsing value for ‘-webkit-text-size-adjust’. Declaration dropped. application.css:3:155 Unknown pseudo-class or pseudo-element ‘-webkit-inner-spin-button’. Ruleset ignored due to bad selector. application.css:3:1425 Unknown pseudo-class or pseudo-element ‘-webkit-search-cancel-button’. Ruleset ignored due to bad selector. application.css:3:1600 Unknown property ‘appearance’. Declaration dropped. application.css:3:2113 Unknown property ‘touch-action’. Declaration dropped. application.css:3:2703 Unknown property ‘user-select’. Declaration dropped. application.css:3:2811 Found invalid value for media feature. application.css:3:3977 Found invalid value for media feature. application.css:3:6787 Unknown property ‘user-select’. Declaration dropped. application.css:3:18012 Unknown property ‘appearance’. Declaration dropped. application.css:3:34344 Unknown pseudo-class or pseudo-element ‘-ms-expand’. Ruleset ignored due to bad selector. application.css:3:34688 Unknown property ‘appearance’. Declaration dropped. application.css:3:35436 Unknown pseudo-class or pseudo-element ‘-ms-input-placeholder’. Ruleset ignored due to bad selector. application.css:3:35883 Unknown pseudo-class or pseudo-element ‘-webkit-input-placeholder’. Ruleset ignored due to bad selector. application.css:3:35981 Unknown property ‘appearance’. Declaration dropped. application.css:3:36316 Unknown pseudo-class or pseudo-element ‘-ms-input-placeholder’. Ruleset ignored due to bad selector. application.css:3:51660 Unknown pseudo-class or pseudo-element ‘-webkit-input-placeholder’. Ruleset ignored due to bad selector. application.css:3:51762 Unknown pseudo-class or pseudo-element ‘-webkit-input-placeholder’. Ruleset ignored due to bad selector. application.css:3:65907 Unknown pseudo-class or pseudo-element ‘-ms-input-placeholder’. Ruleset ignored due to bad selector. application.css:3:66137 Expected ‘none’, URL, or filter function but found ‘progid’. Error in parsing value for ‘filter’. Declaration dropped. application.css:3:82315 Unknown property ‘user-select’. Declaration dropped. application.css:3:107688 Unknown property ‘user-select’. Declaration dropped. application.css:3:116297 Unknown property ‘user-select’. Declaration dropped. application.css:3:123844 Unknown property ‘touch-action’. Declaration dropped. application.css:3:123949 Error in parsing value for ‘cursor’. Declaration dropped. application.css:3:124143 Unknown property ‘touch-action’. Declaration dropped. application.css:3:132886 Unknown property ‘touch-action’. Declaration dropped. application.css:3:133006 Unknown property ‘-moz-border-radius’. Declaration dropped. application.css:3:134100 Unknown property ‘-moz-border-radius’. Declaration dropped. application.css:3:134371 Unknown property ‘over-flow’. Declaration dropped. application.css:3:178565 Unknown property ‘line-spacing’. Declaration dropped. application.css:3:183901 Unknown property ‘speak’. Declaration dropped. application.css:3:190473 Expected declaration but found ‘*’. Skipped to next declaration. application.css:3:242520 Expected declaration but found ‘*’. Skipped to next declaration. application.css:3:242536 Expected declaration but found ‘*’. Skipped to next declaration. application.css:3:243916 Expected declaration but found ‘*’. Skipped to next declaration. application.css:3:243932 Expected ‘none’, URL, or filter function but found ‘progid’. Error in parsing value for ‘filter’. Declaration dropped. application.css:3:245157 Expected ‘none’, URL, or filter function but found ‘progid’. Error in parsing value for ‘filter’. Declaration dropped. application.css:3:245816 Unknown property ‘-moz-osx-font-smoothing’. Declaration dropped. application.css:3:255301 Expected ‘none’, URL, or filter function but found ‘progid’. Error in parsing value for ‘filter’. Declaration dropped. application.css:3:267197 Unknown property ‘background-repeat-x’. Declaration dropped. application.css:3:288746 Unknown property ‘background-repeat-y’. Declaration dropped. application.css:3:288776 Expected ‘none’, URL, or filter function but found ‘progid’. Error in parsing value for ‘filter’. Declaration dropped. application.css:3:295516 Expected ‘none’, URL, or filter function but found ‘progid’. Error in parsing value for ‘filter’. Declaration dropped. application.css:3:295920 Expected ‘none’, URL, or filter function but found ‘progid’. Error in parsing value for ‘filter’. Declaration dropped. application.css:3:296519 Expected ‘none’, URL, or filter function but found ‘progid’. Error in parsing value for ‘filter’. Declaration dropped. application.css:3:296955 Unknown property ‘user-select’. Declaration dropped. application.css:3:297816 Expected ‘none’, URL, or filter function but found ‘progid’. Error in parsing value for ‘filter’. Declaration dropped. application.css:3:297958 Expected ‘none’, URL, or filter function but found ‘progid’. Error in parsing value for ‘filter’. Declaration dropped. application.css:3:298412 Unknown property ‘user-select’. Declaration dropped. application.css:3:299285 Unknown property ‘user-select’. Declaration dropped. application.css:3:321232 Unknown property ‘touch-action’. Declaration dropped. application.css:3:321324 Error in parsing value for ‘cursor’. Declaration dropped. application.css:3:321531 Unknown pseudo-class or pseudo-element ‘-webkit-scrollbar’. Ruleset ignored due to bad selector. application.css:3:322646 Unknown pseudo-class or pseudo-element ‘-webkit-scrollbar’. Ruleset ignored due to bad selector. application.css:3:323389 Expected ‘none’, URL, or filter function but found ‘alpha(’. Error in parsing value for ‘filter’. Declaration dropped. application.css:3:324219 Expected ‘none’, URL, or filter function but found ‘alpha(’. Error in parsing value for ‘filter’. Declaration dropped. application.css:3:327230 Expected ‘none’, URL, or filter function but found ‘alpha(’. Error in parsing value for ‘filter’. Declaration dropped. application.css:3:327492 Expected ‘none’, URL, or filter function but found ‘alpha(’. Error in parsing value for ‘filter’. Declaration dropped. application.css:3:335469 Unknown property ‘speak’. Declaration dropped. homepage-grid.css:1:555 Unknown property ‘-moz-osx-font-smoothing’. Declaration dropped. homepage-grid.css:1:683 Unknown property ‘user-select’. Declaration dropped. homepage-grid.css:1:4774 Unknown property ‘touch-action’. Declaration dropped. homepage-grid.css:1:4815 Error in parsing value for ‘cursor’. Declaration dropped. homepage-grid.css:1:4984 Unknown property ‘font-smoothing’. Declaration dropped. homepage-grid.css:1:6237 Unknown property ‘-moz-border-radius’. Declaration dropped. homepage-grid.css:1:8017 Unknown property ‘-moz-text-shadow’. Declaration dropped. homepage-grid.css:1:8430 Expected ‘none’, URL, or filter function but found ‘progid’. Error in parsing value for ‘filter’. Declaration dropped. homepage-grid.css:1:8977 Expected ‘none’, URL, or filter function but found ‘progid’. Error in parsing value for ‘filter’. Declaration dropped. homepage-grid.css:1:9203 Expected ‘none’, URL, or filter function but found ‘progid’. Error in parsing value for ‘filter’. Declaration dropped. homepage-grid.css:1:10052 Expected ‘none’, URL, or filter function but found ‘progid’. Error in parsing value for ‘filter’. Declaration dropped. homepage-grid.css:1:10282 Expected ‘none’, URL, or filter function but found ‘progid’. Error in parsing value for ‘filter’. Declaration dropped. homepage-grid.css:1:10807 Expected ‘none’, URL, or filter function but found ‘progid’. Error in parsing value for ‘filter’. Declaration dropped. homepage-grid.css:1:11086 Expected ‘none’, URL, or filter function but found ‘progid’. Error in parsing value for ‘filter’. Declaration dropped. homepage-grid.css:1:11352 Expected ‘none’, URL, or filter function but found ‘progid’. Error in parsing value for ‘filter’. Declaration dropped. homepage-grid.css:1:11635 Expected ‘none’, URL, or filter function but found ‘progid’. Error in parsing value for ‘filter’. Declaration dropped. homepage-grid.css:1:26918 Expected ‘none’, URL, or filter function but found ‘progid’. Error in parsing value for ‘filter’. Declaration dropped. homepage-grid.css:1:27398 Expected ‘none’, URL, or filter function but found ‘progid’. Error in parsing value for ‘filter’. Declaration dropped. homepage-grid.css:1:27733 Expected ‘none’, URL, or filter function but found ‘progid’. Error in parsing value for ‘filt

In the console, hide the style warnings (the lines with blue triangles) by clicking the little triangle next to the blue dot and clicking off Warnings. That should declutter it by about 90%.

Hope this helps and works it's 3 am need sleep lol.

Hi makingitbetter, I can't tell what occurred when in relation to the error message, but just skimming through them, none sounds like serious errors that should provoke such a message.

Do you think it could be related to a plugin? While you are troubleshooting this, it might be helpful, to avoid unnecessary pain on sites where Flash is not actually essential, try setting Flash to Click-to-Play ("Ask to Activate"). This will delay Flash from starting on a page until you approve it. (Most other plugins are automatically set to "Ask to Activate.")

To set "Ask to Activate", open the Add-ons page using either:

• Ctrl+Shift+a
• "3-bar" menu button (or Tools menu) > Add-ons

In the left column, click Plugins. Look for "Shockwave Flash" and change "Always Activate" to "Ask to Activate".

With this setting, when you visit a site that wants to use Flash, you should see a notification icon in the address bar and usually (but not always) one of the following: a link in a black rectangle in the page or an infobar sliding down between the toolbar area and the page.

The plugin notification icon in the address bar typically looks like a small, dark gray Lego block. When the page wants to use a blocked plugin, the icon turns red to alert you to the concern.

If you see a good reason to use Flash, and the site looks trustworthy, you can go ahead and click the notification icon in the address bar to allow Flash. You can trust the site for the time being or permanently.

But some pages use Flash only for tracking or playing ads, so if you don't see an immediate need for Flash, feel free to ignore the notification! It will just sit there in case you want to use it later.

jscher2000 said

Hi makingitbetter, I can't tell what occurred when in relation to the error message, but just skimming through them, none sounds like serious errors that should provoke such a message. Do you think it could be related to a plugin? While you are troubleshooting this, it might be helpful, to avoid unnecessary pain on sites where Flash is not actually essential, try setting Flash to Click-to-Play ("Ask to Activate"). This will delay Flash from starting on a page until you approve it. (Most other plugins are automatically set to "Ask to Activate.") To set "Ask to Activate", open the Add-ons page using either:

• Ctrl+Shift+a
• "3-bar" menu button (or Tools menu) > Add-ons

In the left column, click Plugins. Look for "Shockwave Flash" and change "Always Activate" to "Ask to Activate". With this setting, when you visit a site that wants to use Flash, you should see a notification icon in the address bar and usually (but not always) one of the following: a link in a black rectangle in the page or an infobar sliding down between the toolbar area and the page. The plugin notification icon in the address bar typically looks like a small, dark gray Lego block. When the page wants to use a blocked plugin, the icon turns red to alert you to the concern. If you see a good reason to use Flash, and the site looks trustworthy, you can go ahead and click the notification icon in the address bar to allow Flash. You can trust the site for the time being or permanently. But some pages use Flash only for tracking or playing ads, so if you don't see an immediate need for Flash, feel free to ignore the notification! It will just sit there in case you want to use it later.

I did changed it "Shockwave Flash" to "Ask to Activate". like you told me, STILL NO LUCK same problem "Good news and bad news "it's not my computer had the same problem happen on my other windows Xp pro in the front bedroom after updating to 50.0.2 today! for the "Bad news "so now the error happens on both computers now. I also notice a slow lag loading websites on both computers since the update..something is not right !!! but slow performance could have many reasons don't want to point fingers just yet ! might have to live with this until someone finds the real cause of this problem. I also notice someone else posted this problem on windows 7. might be a bigger problem then we think .

problem solved after 50.01.0 update it's been 8 days since update no error popup ! "The procedure entry point strnlen could not be located in the dynamic link library msvcrt.dll"

it's safe to say so far it was fixed by the update.

makingitbetter said

problem solved after 50.1.0 update it's been 8 days since update no error popup ! "The procedure entry point strnlen could not be located in the dynamic link library msvcrt.dll" it's safe to say so far it was fixed by the update.

That was very good work. Well done. Please flag your last post as Solved Problem so others will know.