
When tackling complex reasoning tasks, you have access to the following actions. Use them as needed to progress through your thought process.

[ASSESS]

[ADVANCE]

[VERIFY]

[SIMPLIFY]

[SYNTHESIZE]

[PIVOT]

[OUTPUT]

You should strictly follow the format below:

[ACTION NAME]

# Your action step 1

# Your action step 2

# Your action step 3

...

Next action: [NEXT ACTION NAME]


system
In the Cartesian coordinate system $xOy$, the left and right foci of the ellipse $C_{1}$: $\dfrac {x^{2}}{a^{2}}+ \dfrac {y^{2}}{b^{2}}=1(a > b > 0)$ are $F_{1}$ and $F_{2}$, respectively. $F_{2}$ is also the focus of the parabola $C_{2}$: $y^{2}=4x$. Point $M$ is the intersection of $C_{1}$ and $C_{2}$ in the first quadrant, and $|MF_{2}|= \dfrac {5}{3}$.  
(Ⅰ) Find the equation of $C_{1}$.  
(Ⅱ) For a point $N$ in the plane satisfying $\overrightarrow{MN}= \overrightarrow{MF_{1}}+ \overrightarrow{MF_{2}}$, the line $l$ is parallel to $MN$ and intersects $C_{1}$ at points $A$ and $B$. If $\overrightarrow{OA}\cdot \overrightarrow{OB}=0$, find the equation of line $l$.

Present the answer in LaTex format: \boxed{Your answer}
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