Why are there lots of warnings in the Firefox DevTools and Firebug console?

Question

I have a lot of warnings in the Firefox and the Firebug console. I don't know what to do with them. Are they my fault? Also, how can I make debugging clear and useful in Firefox?

Here are the examples:

[11:06:16.845] function cf does not always return a value @ http://example.hu/jquery.js:16 [11:06:16.853] function ce does not always return a value @ http://example.hu/jquery.js:16 [11:06:16.861] function bZ does not always return a value @ http://example.hu/jquery.js:16 [11:06:16.870] test for equality (==) mistyped as assignment (=)? @ http://example.hu/jquery.js:16 [11:06:16.880] function M does not always return a value @ http://example.hu/jquery.js:16 [11:06:16.889] anonymous function does not always return a value @ http://example.hu/jquery.js:16 [11:06:16.921] test for equality (==) mistyped as assignment (=)? @ http://example.hu/jquery.js:16 [11:06:16.934] anonymous function does not always return a value @ http://example.hu/jquery.js:16 [11:06:16.957] test for equality (==) mistyped as assignment (=)? @ http://example.hu/jquery.js:16 [11:06:16.972] anonymous function does not always return a value @ http://example.hu/jquery.js:17 [11:06:16.998] test for equality (==) mistyped as assignment (=)? @ http://example.hu/jquery.js:17 [11:06:17.012] anonymous function does not always return a value @ http://example.hu/jquery.js:17 [11:06:17.035] test for equality (==) mistyped as assignment (=)? @ http://example.hu/jquery.js:17 [11:06:17.051] anonymous function does not always return a value @ http://example.hu/jquery.js:17 [11:06:17.073] test for equality (==) mistyped as assignment (=)? @ http://example.hu/jquery.js:17 [11:06:17.086] anonymous function does not always return a value @ http://example.hu/jquery.js:17 [11:06:17.126] test for equality (==) mistyped as assignment (=)? @ http://example.hu/jquery.js:18 [11:06:17.153] anonymous function does not always return a value @ http://example.hu/jquery.js:18 [11:06:17.175] reference to undefined property f.valHooks[this] @ http://example.hu/jquery.js:16 [11:06:17.208] reference to undefined property a[f.expando] @ http://example.hu/jquery.js:16 [11:06:17.376] reference to undefined property a[f.expando] @ http://example.hu/jquery.js:16 [11:06:17.480] reference to undefined property a[f.expando] @ http://example.hu/jquery.js:16 [11:06:17.613] reference to undefined property f.event.triggered @ http://example.hu/jquery.js:16

reference to undefined property fbs.breakOnDebugCall
[Break On This Error] var hookReturn = d...e, errorInfo, fbs.breakOnDebugCall);
firebu...vice.js (line 1857)
<System>
reference to undefined property a[f.expando]
[Break On This Error] (function(a,b){function cv(a){return f...ndexOf(".")>=0&&(i=h.split("."),h=i.
jquery.js (line 16)
reference to undefined property fbs.breakOnDebugCall
[Break On This Error] return this.breakOnErrors || fbs.breakOnDebugCall;
firebu...vice.js (line 3523)
<System>
reference to undefined property fbs.breakOnDebugCall
[Break On This Error] var hookReturn = d...e, errorInfo, fbs.breakOnDebugCall);
firebu...vice.js (line 1857)
<System>
reference to undefined property a[f.expando]
[Break On This Error] (function(a,b){function cv(a){return f...ndexOf(".")>=0&&(i=h.split("."),h=i.
jquery.js (line 16)
reference to undefined property fbs.breakOnDebugCall
[Break On This Error] return this.breakOnErrors || fbs.breakOnDebugCall;
firebu...vice.js (line 3523)
<System>
reference to undefined property fbs.breakOnDebugCall
[Break On This Error] var hookReturn = d...e, errorInfo, fbs.breakOnDebugCall);
firebu...vice.js (line 1857)
<System>
reference to undefined property a[f.expando]
[Break On This Error] (function(a,b){function cv(a){return f...ndexOf(".")>=0&&(i=h.split("."),h=i.
jquery.js (line 16)
reference to undefined property fbs.breakOnDebugCall
[Break On This Error] return this.breakOnErrors || fbs.breakOnDebugCall;
firebu...vice.js (line 3523)
<System>
reference to undefined property fbs.breakOnDebugCall
[Break On This Error] var hookReturn = d...e, errorInfo, fbs.breakOnDebugCall);
firebu...vice.js (line 1857)
<System>
reference to undefined property a[f.expando]
[Break On This Error] (function(a,b){function cv(a){return f...ndexOf(".")>=0&&(i=h.split("."),h=i. 

Answer 1

To avoid them to be logged into the Console, you can uncheck Strict Warnings.